feat!: stream image build, pull and push progress

[mokevnin]

images.build, images.pull and images.push returned nil and drained the response, so their progress was lost and a failed build went unnoticed. Docker reports a build failure with status 200 and an error in the last message:

{"stream":" ---> Running in 20f21f18cf3e\n"}
{"error":"...returned a non-zero code: 3","errorDetail":{"code":3,"message":"...returned a non-zero code: 3"}}

• Streaming. The three methods read the stream to the end, yield each typed message to an optional block and raise Errors::StreamError (with detail) on errorDetail or the legacy error. They still read to the end without a block, because a lazily returned stream left unread could cut a pull short.
• Models. New BuildInfo, CreateImageInfo, PushImageInfo, ErrorDetail, ProgressDetail and ImageID, from the definitions in the Engine API. BuildInfo#aux is ImageID | String: the classic builder sends an image id, BuildKit a trace.
• Internal::JSONLStream. The existing request(stream:) now gets the raw lines, because Docker sends its progress streams as application/json and decode_content would join them into one document.
• BuildKit. Helpers::BuildkitStatus.decode reads the base64 protobuf StatusResponse (moby/buildkit control.proto): vertexes and logs. PlainPrinter renders it as --progress=plain does:

  #4 [2/2] RUN echo from-sdk
  #4 from-sdk
  #4 DONE
  

• Fix in Union#coerce. The error of a failed variant attempt survived a later variant matching, so reading BuildInfo#aux as a String raised. Each attempt now starts clean, and the chosen alternative keeps its own error.

Checked against Docker Engine 29.8 (API 1.56): pull, a BuildKit build with its log, a failing build raising StreamError, and a push to a local registry:2. The BuildKit test decodes messages captured from that daemon.

rake lint (rubocop, Sorbet, Steep) and rake test (189 runs, 0 failures) pass.

🤖 Generated with Claude Code