Rewind request bodies before retry

[ioquatix]

Summary

• Use request.rewind! before retrying requests known not to have been processed (Protocol::HTTP::RefusedError).
• Use request.retry! before retrying ambiguous connection failures.
• Require released protocol-http ~> 0.64 for the retry preparation API.
• Add focused client retry tests proving consumed request bodies are resent on retry.

Testing

• bundle exec sus test/async/http/client.rb
• bundle exec sus

Full suite result: 231 passed, 3 skipped.