Make byte fixtures checkout-stable and run tests on Windows CI #355

Description

A normal Windows checkout with core.autocrlf=true changes tests/sample_file.txt from LF to CRLF, but the base64 transform test asserts the LF byte sequence. This makes both sync and async variants fail on a supported OS.

The CI workflow only runs tests on Ubuntu, so this Windows-specific failure is not detected before merge/release.

Reproduction

On Windows:

git config core.autocrlf true
git checkout .
python -m pytest -o addopts="" tests/test_transform.py -k base64_file_input

Observed failures:

# actual bytes include CRLF
SGVsbG8sIHdvcmxkIQ0K

# expected bytes include LF
SGVsbG8sIHdvcmxkIQo=

git ls-files --eol tests/sample_file.txt reports:

i/lf w/crlf attr/ tests/sample_file.txt

There is no .gitattributes rule making this byte fixture checkout-stable.

Code references

• Byte fixture: tests/sample_file.txt
• Exact base64 assertion: tests/test_transform.py:419-426
• Linux-only test runner: .github/workflows/ci.yml:76-94

Expected behavior

Tests should pass on every supported development platform. The fixture should be treated as binary or forced to LF with .gitattributes, and a Windows CI job should cover platform-specific code and checkout behavior.

Actual behavior

The two test_base64_file_input cases fail on a standard Windows Git checkout, while Ubuntu-only CI remains green.

Why this matters

The project declares Windows support and ships a Windows-specific SEA binary. Without Windows CI, both portable test-fixture problems and Windows-only lifecycle/packaging regressions can ship unnoticed.

Prior-art check

I searched open/closed issues and PRs for this fixture, CRLF/autocrlf, Windows pytest failures, and Windows CI and found no existing report.