Add blaise_thread.pas runtime unit wrapping pthread_create, pthread_join,
pthread_mutex_init/lock/unlock/destroy and sysconf for GetCPUCount.
Implement TThread (Create, Start, Terminate, WaitFor, Execute virtual,
FreeOnTerminate) and TCriticalSection (Enter/Leave) in classes.pas using
ARC-safe ref counting in the thread trampoline.
Fix EmitFieldCleanupFn to walk the parent chain when emitting the Destroy
call — previously a subclass without its own Destroy would generate an
empty cleanup, causing leaked resources from parent destructors.
Link -lpthread in both the compiler driver and E2E test base.
Include 7 E2E tests covering basic execution, WaitFor blocking, Terminate
flag, Finished flag, multiple threads, mutex-protected counter, and
inherited Destroy cleanup.
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