Sign Assembly cancellations with the originating client

[tim-kos]

Response::Assembly#cancel! currently sends an unsigned DELETE, so cancellation fails for Workspaces that require correct signatures.

Responses returned by Assembly#create!, get, and replay retain their originating client. Cancellation includes its auth parameters and signs with its secret when configured; each signed cancellation receives a fresh nonce. Authentication survives response replacement and reloads. Directly constructed responses without a client preserve their existing unsigned behavior.

Validation: full Ruby 3.3 suite passes (128 tests, 265 assertions; optional live-upload and signature-parity tests skipped), plus bundle exec standardrb and git diff --check. Tests check the actual outgoing HMAC for created and fetched Assemblies, replayed responses, fresh nonces, and clients without a secret. Existing direct-response cancellation coverage also passes.

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.

Also make the existing rate-limit warning assertion tolerate unrelated dependency deprecation messages. The Ruby 3.4 CI seed that exposed it (30047) passes locally after the assertion change.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.42%. Comparing base (79535b2) to head (5be4bfc).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #86      +/-   ##
==========================================
+ Coverage   99.40%   99.42%   +0.01%     
==========================================
  Files           9        9              
  Lines         336      345       +9     
  Branches       38       40       +2     
==========================================
+ Hits          334      343       +9     
  Misses          1        1              
  Partials        1        1              

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