fix: include tests in sdist

[Lovlace777]

Summary

• Includes the test suite and root conftest.py in the source distribution.
• Keeps the wheel contents unchanged.
• Fixes the packaging gap reported in sdist is missing tests #1092 so downstream packagers can run tests from the sdist.

Validation

• python -m hatchling build -t sdist -d ..\tmp\syrupy-baseline-sdist before the change showed 0 tests/ entries and no root conftest.py in the sdist.
• python -m hatchling build -t sdist -d ..\tmp\syrupy-final-sdist passed after the change.
• Tarball inspection after the change found 187 tests/ entries, root conftest.py, tests/conftest.py, and representative test files in the sdist.
• python -X utf8 -m pytest tests -q passed: 376 passed, 60 xfailed, 6 xpassed.
• git diff --check passed.

Notes

• Closes sdist is missing tests #1092.
• No runtime package or wheel content changes are intended.

[noahnu]

I'm not too familiar with why it's valuable to add tests to the sdist. What's the use case?

Do we also need to ensure folks running these tests install the relevant test dependencies? Or is that something we put in the documentation?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@           Coverage Diff           @@
##             main    #1099   +/-   ##
=======================================
  Coverage   97.37%   97.37%           
=======================================
  Files          24       24           
  Lines        1717     1717           
=======================================
  Hits         1672     1672           
  Misses         45       45           

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[noahnu]

I did some further research on this, I think it's fine