Add WebSocket client metrics

[LivingLikeKrillin]

Summary

Add metrics support for WebSocket clients, including handshake time,
data received/sent, connection duration, and error counting.

• Add constants, meter/observation documentation, and recorder interfaces
  with Micrometer-based implementation
• Add channel handlers that replace the HTTP metrics handler on WebSocket
  upgrade and track connection duration via handler lifecycle
• Exclude control frames (Close, Ping, Pong) from data metrics

Test plan

• Handshake time timer
• Data received time and distribution summary
• Data sent time and distribution summary
• Connection duration timer
• Multiple connections aggregation
• URI tag value normalization function
• Handshake failure scenario
• HTTP/1.1 and H2 protocol combinations

Related to #3820

[violetagg]

@LivingLikeKrillin On most classes you have @author raccoonback is that the correct author? Also the copyright is 2025 while it should be 2026, also change the @since 1.3.2 to 1.3.5

[violetagg]

Thanks for the PR!
I started with the review. Can you please resolve the issues that I've identified till now?

[violetagg]

I have proposal for moving handshake timer to the abstract class so that it is available for all handlers. What do you think?

[violetagg]

Please also ensure you have Signed-off-by so that we have a happy DCO check

[LivingLikeKrillin]

Hi @violetagg, round 3 changes are pushed. Here's what was addressed:

• ✅ Handshake timer moved to AbstractWebSocketClientMetricsHandler —
  handshakeStartTime, startHandshake, recordHandshakeComplete, and
  recordHandshakeFailure now live in the abstract class.
• ✅ MicrometerWebSocketClientMetricsHandler now calls
  super.startHandshake(channel) and keeps only the Micrometer Observation
  setup on top. recordHandshakeComplete/recordHandshakeFailure are
  overridden to stop the Observation instead of invoking the recorder, as the
  Observation replaces recorder-based handshake time recording.
• ✅ ContextAwareWebSocketClientMetricsHandler overrides
  recordHandshakeComplete and recordHandshakeFailure to pass contextView
  to the recorder.
• ✅ micrometerWsHandler field type in WebsocketClientOperations
  changed to AbstractWebSocketClientMetricsHandler, since the handshake
  timer is now available for all variants.
• ✅ Micrometer branch in swapMetricsHandler simplified to only
  construct the new handler, matching your suggestion.
• ✅ DefaultWebSocketClientMetricsRecorder wrapper added to wrap a plain
  HttpClientMetricsRecorder when the user supplies a non-WebSocket-aware
  recorder, mirroring the context-aware pattern.
• ✅ Unused parameters removed from AbstractWebSocketClientMetricsHandler
  — ctx from recordConnectionClosed and recordException, and channel
  from recordRead, as suggested.
• ✅ path and contextView fields in
  AbstractWebSocketClientMetricsHandler are now final.

The DCO check is green. Could you take another look when you have a moment?

[LivingLikeKrillin]

Thanks for picking up the copyright and unused-import cleanup directly.

The remaining CI failure was NativeConfigTest.testChannelHandler() — the new WebSocket ChannelHandler classes weren't registered in reflect-config.json for GraalVM native image. Pushed b48178d8 to add them:

• AbstractWebSocketClientMetricsHandler
• ContextAwareWebSocketClientMetricsHandler
• MicrometerWebSocketClientMetricsHandler
• WebSocketClientMetricsHandler

Verified locally by running the same commands CI does:

• ./gradlew clean spotlessCheck -PspotlessFrom=origin/main — PASS
• ./gradlew clean japicmp — PASS
• ./gradlew :reactor-netty-http:check -PforceTransport=nio (with the Java 8 flags) — PASS, no flakes

Ready for another CI run.