test: 添加时区相关方法的单元测试

添加三个测试用例验证 TimerHelper 中时区相关方法的正确性：
1. TimeToWithTimeZone_ShouldHandleDifferentKinds：测试 TimeToSecondsWithTimeZone 和 TimeToMillisecondsWithTimeZone 方法对不同 DateTime.Kind 的处理
2. ExtendedMethods_ShouldIncludeOffset：测试扩展的 Day/Week/Month/Year 的 WithTimeZone 方法是否包含时区偏移
3. AllWithTimeZoneMethods_ShouldIncludeOffset：全面测试所有 WithTimeZone 方法是否都正确应用时区偏移

Author: AlianBlank

GameFrameX.Foundation.Tests/Utility/TimerHelperTimeZoneTests.cs

@@ -223,5 +223,121 @@ public void UnixTimeWithTimeZone_ShouldIncludeOffset()
             // 允许误差在 100 毫秒内
             Assert.True(Math.Abs(diffMilliseconds - 28800000) <= 100, $"Expected diff 28800000, but got {diffMilliseconds}");
         }
+
+        /// <summary>
+        /// 测试 TimeToSecondsWithTimeZone 和 TimeToMillisecondsWithTimeZone 方法
+        /// </summary>
+        [Fact]
+        public void TimeToWithTimeZone_ShouldHandleDifferentKinds()
+        {
+            var offset = TimeSpan.FromHours(8);
+            var customTimeZone = TimeZoneInfo.CreateCustomTimeZone("Test+8", offset, "Test+8", "Test+8");
+            TimerHelper.SetTimeZone(customTimeZone);
+
+            var nowUtc = DateTime.UtcNow;
+            var nowLocal = DateTime.Now; // System Local
+            // 构造一个 Unspecified 时间，假设它就是 CurrentTimeZone 下的时间
+            var nowZone = TimeZoneInfo.ConvertTimeFromUtc(nowUtc, customTimeZone); // Kind is Unspecified
+
+            // 1. Test UTC input
+            // 预期：UTC 时间戳 + 8 小时
+            var expectedSeconds = new DateTimeOffset(nowUtc).ToUnixTimeSeconds() + 28800;
+            var actualSecondsUtc = TimerHelper.TimeToSecondsWithTimeZone(nowUtc);
+            Assert.Equal(expectedSeconds, actualSecondsUtc);
+
+            // 2. Test Unspecified input (assumed as CurrentTimeZone)
+            // nowZone 是 UTC+8 的时间，转回 UTC 应该是 nowUtc
+            // 所以结果应该和上面一样
+            var actualSecondsZone = TimerHelper.TimeToSecondsWithTimeZone(nowZone);
+            Assert.Equal(expectedSeconds, actualSecondsZone);
+
+            // 3. Test System Local input
+            // TimerHelper should convert System Local to UTC, then apply CurrentTimeZone offset
+            // So result should still be same absolute moment + 8 hours
+            // 注意：如果 System Local 和 UTC 转换有微小差异（如 tick 精度），可能会有一点点误差，但在秒级应该是相等的
+            var actualSecondsLocal = TimerHelper.TimeToSecondsWithTimeZone(nowLocal);
+            // nowLocal 和 nowUtc 代表同一时刻（理想情况下）
+            // 允许 1 秒误差
+            Assert.True(Math.Abs(actualSecondsLocal - expectedSeconds) <= 1);
+        }
+
+        /// <summary>
+        /// 测试扩展的 Day/Week/Month/Year 的 WithTimeZone 方法
+        /// </summary>
+        [Fact]
+        public void ExtendedMethods_ShouldIncludeOffset()
+        {
+            var offset = TimeSpan.FromHours(8);
+            var customTimeZone = TimeZoneInfo.CreateCustomTimeZone("Test+8", offset, "Test+8", "Test+8");
+            TimerHelper.SetTimeZone(customTimeZone);
+
+            long offsetSeconds = (long)offset.TotalSeconds;
+
+            // 1. Test Day
+            var todayStandard = TimerHelper.GetTodayStartTimestamp();
+            var todayWithZone = TimerHelper.GetTodayStartTimestampWithTimeZone();
+            Assert.Equal(offsetSeconds, todayWithZone - todayStandard);
+
+            // 2. Test Week
+            var weekStandard = TimerHelper.GetWeekStartTimestamp();
+            var weekWithZone = TimerHelper.GetWeekStartTimestampWithTimeZone();
+            Assert.Equal(offsetSeconds, weekWithZone - weekStandard);
+
+            // 3. Test Month
+            var monthStandard = TimerHelper.GetMonthStartTimestamp();
+            var monthWithZone = TimerHelper.GetMonthStartTimestampWithTimeZone();
+            Assert.Equal(offsetSeconds, monthWithZone - monthStandard);
+
+            // 4. Test Year
+            var yearStandard = TimerHelper.GetYearStartTimestamp();
+            var yearWithZone = TimerHelper.GetYearStartTimestampWithTimeZone();
+            Assert.Equal(offsetSeconds, yearWithZone - yearStandard);
+            
+            // 5. Test specific date (Month End)
+            var now = DateTime.UtcNow;
+            var monthEndStandard = TimerHelper.GetEndTimestampOfMonth(now);
+            var monthEndWithZone = TimerHelper.GetEndTimestampOfMonthWithTimeZone(now);
+            Assert.Equal(offsetSeconds, monthEndWithZone - monthEndStandard);
+        }
+
+        [Fact]
+        public void AllWithTimeZoneMethods_ShouldIncludeOffset()
+        {
+            var offset = TimeSpan.FromHours(8);
+            var customTimeZone = TimeZoneInfo.CreateCustomTimeZone("Test+8", offset, "Test+8", "Test+8");
+            TimerHelper.SetTimeZone(customTimeZone);
+            long offsetSeconds = (long)offset.TotalSeconds;
+            var now = DateTime.UtcNow;
+
+            // Day
+            Assert.Equal(offsetSeconds, TimerHelper.GetTodayStartTimestampWithTimeZone() - TimerHelper.GetTodayStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetTodayEndTimestampWithTimeZone() - TimerHelper.GetTodayEndTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetStartTimestampOfDayWithTimeZone(now) - TimerHelper.GetStartTimestampOfDay(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetEndTimestampOfDayWithTimeZone(now) - TimerHelper.GetEndTimestampOfDay(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetTomorrowStartTimestampWithTimeZone() - TimerHelper.GetTomorrowStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetTomorrowEndTimestampWithTimeZone() - TimerHelper.GetTomorrowEndTimestamp());
+
+            // Week
+            Assert.Equal(offsetSeconds, TimerHelper.GetWeekStartTimestampWithTimeZone() - TimerHelper.GetWeekStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetWeekEndTimestampWithTimeZone() - TimerHelper.GetWeekEndTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetStartTimestampOfWeekWithTimeZone(now) - TimerHelper.GetStartTimestampOfWeek(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetEndTimestampOfWeekWithTimeZone(now) - TimerHelper.GetEndTimestampOfWeek(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetNextWeekStartTimestampWithTimeZone() - TimerHelper.GetNextWeekStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetNextWeekEndTimestampWithTimeZone() - TimerHelper.GetNextWeekEndTimestamp());
+
+            // Month
+            Assert.Equal(offsetSeconds, TimerHelper.GetStartTimestampOfMonthWithTimeZone(now) - TimerHelper.GetStartTimestampOfMonth(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetEndTimestampOfMonthWithTimeZone(now) - TimerHelper.GetEndTimestampOfMonth(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetNextMonthStartTimestampWithTimeZone() - TimerHelper.GetNextMonthStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetNextMonthEndTimestampWithTimeZone() - TimerHelper.GetNextMonthEndTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetMonthStartTimestampWithTimeZone() - TimerHelper.GetMonthStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetMonthEndTimestampWithTimeZone() - TimerHelper.GetMonthEndTimestamp());
+
+            // Year
+            Assert.Equal(offsetSeconds, TimerHelper.GetYearStartTimestampWithTimeZone() - TimerHelper.GetYearStartTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetYearEndTimestampWithTimeZone() - TimerHelper.GetYearEndTimestamp());
+            Assert.Equal(offsetSeconds, TimerHelper.GetStartTimestampOfYearWithTimeZone(now) - TimerHelper.GetStartTimestampOfYear(now));
+            Assert.Equal(offsetSeconds, TimerHelper.GetEndTimestampOfYearWithTimeZone(now) - TimerHelper.GetEndTimestampOfYear(now));
+        }
     }
 }