Fix stdio server newline translation on Windows

[yyzquwu]

Summary

• Disable Windows CRLF translation in stdio_server() by setting newline="" on the default stdio wrappers.
• Add a regression test for the default stdout path so JSON-RPC frames stay LF-only.

Fixes #2433.

Verification

Windows 11, Python 3.13.13:

tests/server/test_stdio.py::test_stdio_server PASSED
tests/server/test_stdio.py::test_stdio_server_uses_lf_newlines_with_default_stdout PASSED
tests/server/test_stdio.py::test_stdio_server_invalid_utf8 PASSED
3 passed

b'{"jsonrpc":"2.0","id":3,"method":"ping"}\n'

Branch coverage for tests/server/test_stdio.py: 100.00%.

Codex review passed before commit.