Vendored PreparedStatementThreadTest passes when the race throws a runtime exception #118

The #51 divergence in PreparedStatementThreadTest.testRace rethrows only AssertionError. Any other cause is swallowed, including NullPointerException, IndexOutOfBoundsException, and ConcurrentModificationException. These are the Java equivalent of the native crash the test exists to catch.

When queryThread.get() throws, closeThread.get() is never awaited.

This test guards #89, which serializes statement close and execute. A close and execute race that throws an NPE inside LibsqlResultSet still passes.

Expected:

• Tolerate only an SQLException cause. Rethrow everything else.
• Always await both futures.
• Record the narrower divergence in the manifest.