fix(distribution): stop the release spinner printing "null%"

[bhdnb]

crowdin distribution release <hash> printed a progress line reading Releasing distribution <hash>: null% on its way to a successful release.

The poll loop in DistributionService guarded the progress callback with release.progress !== undefined, but this endpoint sends progress: null while a release is pending. null !== undefined is true, so the null reached DistributionCommand's spinner message and rendered as the literal "null%".

Fixed in two places, not one. The guard becomes != null, and ReleaseStatus.progress is widened to number | null. With the old progress?: number, TypeScript sees number | undefined, which makes != null and !== undefined look equivalent -- the narrow type is what made the original guard look correct, and leaving it would invite the next reader to simplify the fix straight back out.

The three existing releaseDistribution tests all mocked progress as a number, which is why this survived. Added one that polls null -> null -> 40 -> success and requires the callback to receive [40]. Confirmed it has teeth: with the guard reverted it fails on [null, null, 40].

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.20%. Comparing base (aeb670b) to head (b95ffe4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1100   +/-   ##
=======================================
  Coverage   92.20%   92.20%           
=======================================
  Files         141      141           
  Lines       11485    11485           
=======================================
  Hits        10589    10589           
  Misses        896      896           

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[bhdnb]

Unrelated to this PR: the checkVersion test started failing unexpectedly. The fix is minimal, so I’ve included it here.