Fix encoding mismatch between python child process and uv

[kahojyun]

Summary

This PR fixes #7733. According to CPython documentation on sys.stdout, when stdout/stderr is non-character device like pipe, the encoding will be set to system locale on windows. However, on the Rust side stdout_reader and stderr_reader expect them to be encoded in UTF-8 and will fail when child process write non-ASCII character to stdout/stderr, e.g., build directory name containing non-ASCII character.

Both CPython3 and PyPy support environment variable PYTHONIOENCODING. When it is set to utf-8, python will use UTF-8 encoding for stdin/stdout/stderr. Since stdin is not used by the spawned python process and we expect stdout/stderr to use UTF-8, this fix should work as expected.

Test Plan

I only tested it on my computer with CPython 3.12 and 3.7. With the fix applied I confirmed that the case I described is fixed.

I'm using Windows 11 with system locale set to code page 936.

[charliermarsh]

\cc @BurntSushi

[BurntSushi]

This sounds right to me. Nice catch.

[charliermarsh]

Great find, thanks!