fix(funasr): fix race condition in suppress_stdout causing startup crash

[wei-yao]

Problem

On startup, FunASR models finish loading but the server immediately crashes with:

ValueError: I/O operation on closed file
  File "funasr_server.py", line 471, in run
    print(json.dumps(init_result, ensure_ascii=False))

The app gets stuck showing "模型加载中" indefinitely.

Root Cause

suppress_stdout() saves and restores the global sys.stdout to suppress noise from FunASR/modelscope during model initialization. Since three models (ASR, VAD, punc) load in parallel threads, each thread calls suppress_stdout() concurrently — causing a race condition:

Step	Thread A (ASR)	Thread B (VAD)	sys.stdout
1	old_A = sys.stdout (real pipe)		real pipe
2	sys.stdout = devnull_A		devnull_A
3		old_B = sys.stdout → captures devnull_A	devnull_A
4		sys.stdout = devnull_B	devnull_B
5	(done) sys.stdout = old_A, devnull_A.close()		real pipe
6		(done) sys.stdout = old_B → closed devnull_A ❌	closed file

After all threads complete, sys.stdout points to a closed file, so any subsequent print() raises ValueError.

Fix

Restore to sys.__stdout__ (Python's original stdout) instead of the locally saved reference. This is always stable regardless of thread interleaving.

# before
finally:
    sys.stdout = old_stdout
    devnull.close()

# after
finally:
    sys.stdout = sys.__stdout__
    devnull.close()