🐛 fix(test): resolve flaky write non-starvation test (#490)

The test only signaled the last reader's release event and relied on
chain propagation, but the 3-second join timeout was too tight for
PyPy on macOS where process spawn and SQLite operations are slower.

Signal all reader release events explicitly and increase the join
timeout to 10 seconds to accommodate slower runtimes.

Author: gaborbernat

tests/test_read_write.py

@@ -256,7 +256,7 @@ def test_write_non_starvation(lock_file: str) -> None:
             event.set()
 
         for idx, reader in enumerate(readers):
-            reader.join(timeout=3)
+            reader.join(timeout=10)
             assert not reader.is_alive(), f"Reader {idx} did not exit cleanly"