AOF Persistence Updates

[UdeshyaDhungana]

Note

Low Risk
Low risk because changes are confined to the tester harness and fixtures, with only minor process lifecycle guarding in RedisExecutable.Kill().

Overview
AOF tests now validate appendfsync. Default AOF config assertions include CONFIG GET appendfsync (expects everysec), and flag-based tests pass --appendfsync and verify it via CONFIG GET.

Filesystem expectations around AOF directories are tightened. Adds DirDoesNotExistAssertion and expands the AOF directory creation test to also assert the default appendonlydir is not created when appendonly is off, including updated fixtures.

Improves executable lifecycle handling in tests. RedisExecutable now tracks isRunning to make Kill() idempotent, enabling mid-test terminate/restart patterns without spurious kill attempts.

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