Address review: GIL-safe logging callback, None-init, env guard, test
- Initialize the global callback to py::none() in the sink factory so the
no-callback fast path is taken before any callback is set (a null handle is
not None, so the previous code could invoke an empty callable).
- Restructure PythonCallbackSink::SendImpl to acquire the GIL before copying or
destroying the py::object, avoiding Python refcount mutation on non-Python
worker threads. Lock order is GIL -> mutex consistently.
- Only update default logger severity when installing a callback; resetting
with None no longer silently overwrites a user-set severity.
- Drop the unused err_msg in the exception handler.
- Skip replacing the LoggingManager when a process-wide OrtEnv already existed
(created outside Python) to avoid invalidating by existing
sessions.
- Assert the callback is actually invoked and validate record types in the test.
- Reorder __init__.py import alphabetically; add trailing newline to header.