Two test failures from the comparator rewrite:
1. "different unparseable strings → newer" was useful — branch-name
builds (e.g. PackageInfo reports 'main' while server reports
'dev') should still surface the banner so the operator sees that
something is misaligned. Restore that fallback: if both sides
parse to all-zero components (no numeric structure on either),
compare as strings.
2. "honors prerelease ordering" tested pub_semver behavior we no
longer use. Replaced with tests that cover what the new
comparator actually does: zero-padding for length mismatch,
leading-zero normalization, 4-part date+build comparisons, and
month-rollover correctness without leading zeros.
bvandeusen
74cc76b369