fix: add future annotations to test files for Python 3.9 compat

Author: medeirosdev

tests/test_harvesters.py

@@ -14,6 +14,8 @@
 #
 # =============================================================================
 
+from __future__ import annotations
+
 """Tests for the entropy harvesters."""
 
 import pytest

tests/test_integration.py

@@ -11,6 +11,8 @@
 #
 # =============================================================================
 
+from __future__ import annotations
+
 """Integration tests for the TrueEntropy library."""
 
 import time

tests/test_pool.py

@@ -12,6 +12,8 @@
 #
 # =============================================================================
 
+from __future__ import annotations
+
 """Tests for the EntropyPool class."""
 
 import threading

tests/test_tap.py

@@ -13,6 +13,8 @@
 #
 # =============================================================================
 
+from __future__ import annotations
+
 """Tests for the EntropyTap class."""
 
 import math