feat: add support for Python metadata version 2.5

[nodivbyzero]

Summary

• Add support for parsing Python packages with metadata version 2.5
• Version 2.5 uses the same headers as 2.4 (PEP 639 finalized)
• Add unit tests for metadata version handling in internal/distributions/

Fixes CI failure in https://github.com/rstudio/python-distribution-parser/actions/runs/31545855913/job/93958054499?pr=81 where hatch wheels with metadata version 2.5 failed to parse.

Test plan

• go build ./... passes
• go test ./internal/distributions/ passes with new unit tests
• CI workflow runs all tests including the hatch wheel integration test

[posit-snyk-bot]

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[glin]

👍, once this gets into PPM do you think we need a NEWS item? I remember last time we bumped to 2.4, it was because of some python builder bug.

[nodivbyzero]

@glin When we updated PPM to v0.7.0, there was a metadata version change and a breaking change - the MD5Digest field was removed. We didn't update NEWS.md to reflect that.