Fix Assembly polling after status rate limits

[tim-kos]

Assembly status polling currently treats ASSEMBLY_STATUS_FETCHING_RATE_LIMIT_REACHED as a terminal failure and loses the status URL when that response replaces the previous body. Subsequent reloads can then request the API root.

Retain the status URL across response replacement, keep status rate limits out of finished?, and wait at least the server’s info.retryIn before retrying. Preserve the existing one-second polling interval and tries limit. Reject reloads without a status URL before issuing a request, and keep response parsing lazy.

Validation: full Ruby 3.3 suite passes (128 tests, 257 assertions; optional live-upload and signature-parity tests skipped), plus bundle exec standardrb and git diff --check. Regression tests cover automatic recovery, manual reloads, missing retry metadata, exhausted tries, and missing status URLs.

Compatibility: constrain JSON to versions below 3 because Ruby 3.1 resolves MultiJson 1.19, whose positional parsing options are incompatible with JSON 3. This dependency constraint is shared across the four independent fixes.

The four fixes also merge together cleanly. Their combined Ruby 3.3 suite passes with Node signature parity enabled: 147 tests, 321 assertions, with only the optional live upload skipped.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.42%. Comparing base (79535b2) to head (3f47189).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   99.40%   99.42%   +0.01%     
==========================================
  Files           9        9              
  Lines         336      345       +9     
  Branches       38       41       +3     
==========================================
+ Hits          334      343       +9     
  Misses          1        1              
  Partials        1        1              

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