[TST]: Defer cross-version test collection

[rescrv]

Description of changes

Move version discovery out of module import into
pytest_generate_tests so spawned writer children no longer
depend on a fresh PyPI request at startup.

Assert the writer process exits cleanly and close the
multiprocessing connections in a finally block so failures
surface instead of leaking resources.

Test plan

CI

Migration plan

N/A

Observability plan

N/A

Documentation Changes

N/A

Co-authored-by: AI

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Testing, Bugs, Errors, Logs, Documentation

• Can you think of any use case in which the code does not behave as intended? Have they been tested?
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• If appropriate, are there adequate property based tests?
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