logging_subprocess deadlocks on Windows when child stdout/stderr exceeds pipe buffer #519

Problem

logging_subprocess in github_backup/github_backup.py opens child processes with stdout=PIPE, stderr=PIPE but never drains those pipes on Windows, causing git clone / git fetch of any repo producing more than a few KB of output to hang indefinitely.

Steps

1. On Windows, run github-backup <user> --all -o backup/ against any account with a repo whose clone produces substantial stderr progress output.
2. Observe process hangs at the first large git clone or git fetch.

Expected

Process completes; child output is either drained silently or logged.

Actual

The parent's while child.poll() is None: check_io() loop spins forever because check_io() returns immediately on win32 (github_backup/github_backup.py:102-103) while the child's PIPE buffers fill and block the git subprocess.

Environment

• github-backup 0.63.0 (github_backup/__init__.py:1)
• Windows, Python 3.10+ (per pyproject.toml)

Cite: github_backup/github_backup.py:91-114. Fix idea: drain stdout/stderr with threads on Windows, or pass stdout=None, stderr=None when sys.platform == "win32" so the child inherits the parent's handles instead of buffering into a never-read PIPE.

Thanks for maintaining josegonzalez/python-github-backup!