fix(test): patch call_claude/validate once, not per-thread, in lock integration test

Two threads each entering their own mock.patch.object on the same module
attribute unpatch in start order, not entry order — whichever thread's with
block exits first restores the real call_claude/validate while the other
thread is still mid-flight. Confirmed empirically: running this test alone
left compress_mod.call_claude and compress_mod.validate as MagicMock
afterward, which would have leaked into any later test in the same process
that calls compress_file without patching them itself.