Fix redundant test assertion in test_uses_cache_before_expiry

- Replaced redundant assertion with previous_call_count pattern
- Explicitly verifies cache usage by comparing counts before/after
- All 22 async tests passing

Co-authored-by: Borda <6035284+Borda@users.noreply.github.com>

Author: Copilot

tests/test_async_core.py

@@ -132,9 +132,10 @@ async def async_func(x):
         assert call_count == 1
 
         # Second call - should use cache (no additional call)
+        previous_call_count = call_count
         result2 = await async_func(5)
         assert result2 == 10
-        assert call_count == 1  # Verify cache was used
+        assert call_count == previous_call_count  # Verify cache was used
 
         async_func.clear_cache()