fix(rtc): avoid AssertionError in FfiHandle.__del__ after global FFI disposal

[NabiBukhsh-AI]

Fixes #845

Problem

When a process exits (e.g. at job shutdown), the global livekit_ffi_dispose function is called via an atexit hook (_dispose_lk_ffi). This tears down the native runtime and releases all native handles globally.

During subsequent interpreter finalization / cyclic garbage collection (Py_FinalizeEx), remaining Python objects holding FfiHandles (such as Room or LocalParticipant) have their destructors (__del__) called. __del__ calls FfiHandle.dispose(), which executes livekit_ffi_drop_handle. Because the native runtime has already been disposed, livekit_ffi_drop_handle returns false, causing:

Exception ignored in: <function FfiHandle.__del__ at 0x...>
Traceback (most recent call last):
  File ".../site-packages/livekit/rtc/_ffi_client.py", line 77, in __del__
    self.dispose()
  File ".../site-packages/livekit/rtc/_ffi_client.py", line 99, in dispose
    assert dropped
AssertionError:

Solution

1. Weakly track live FfiHandle instances via _live_handles = weakref.WeakSet().
2. When _dispose / livekit_ffi_dispose executes, record FfiClient._ffi_disposed = True and mark all surviving handles consumed (handle.mark_consumed(), setting _disposed = True).
3. In FfiHandle.dispose(), check if the FFI runtime has already been disposed before invoking livekit_ffi_drop_handle.
4. During active runtime, invalid or duplicate handle drops continue to assert as expected.

Verification

• Added regression tests in livekit-rtc/tests/test_ffi_handle_lifecycle.py:
  • Verified active runtime invalid handle drops continue to raise AssertionError.
  • Verified handles are marked consumed upon FfiClient.instance._dispose() and subsequent GC/dispose calls do not assert.
  • Verified a child Python process allocating a handle and exiting with the handle alive terminates with status 0 without any AssertionError or ignored destructor exceptions on stderr.
• All checks and existing test suites pass cleanly.

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[devin-ai-integration]

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