tests: dedup shared fixtures into test_utils::helpers (#907)

[wboayue]

Closes #907. Covers the issue body plus the items from @tradatious's comment.

Moved to common::test_utils::helpers:

• binary_text (4 copies) and body (2), with body now built on binary_text; 2 hand-written frames in connection/common_tests.rs switched to binary_text
• handshake_response_frame(server_version, zone): replaces 13 hand-written handshake strings across client/connection/transport tests
• handshake_frames(server_version, zone, next_order_id): the client tests' handshake_frames() and the connection tests' push_handshake_in_zone now share it. push_handshake* stay per file because sync and async MemoryStream are different types.
• FARM_OK_MSG, farm_ok_frame_unrouted, farm_ok_frame_42
• execution_data_frame: replaces the hand-built execution_data_body proto with the execution_data() builder
• NoticeTestData, CapturingSink (adds a notices() snapshot accessor)
• test_notice(code, msg): replaces 5 constructors (test_notice ×3, make_notice, notice_with_code). It delegates to Notice::synthesized but keeps a separate name, so tests that use real TWS codes don't read like tests of client-generated notices.

Not changed:

• the protobuf frame in test_parse_raw_message_protobuf: its payload is raw proto bytes, not text, and the test checks the raw protobuf parse path
• DeclaresTickPrice: each copy is paired with its own static CALL_COUNT counter inside the test. With --all-features, the sync and async tests run in parallel in one binary, so a shared counter would race.

Test-only. Ran clippy --all-targets -D warnings and cargo test --lib for default, --features sync and --all-features, plus cargo fmt --check.