Attempt to fix logging race

[jopemachine]

I'm trying to fix the logging race occurred when integrating raftify with Backend.AI, but it is still incomplete method currently.

[jopemachine]

I think the best solution at this point is to write the slog log to a file instead of standard output, so that it doesn't compete with the Python logger at all.

Writing a PyMutex binding to check if slog's standard output is locked every time in Python is too overheady, requires fixing every Python log call to an asynchronous function, and is unnecessary, in my opinion.