node:http server does not publish to HTTP server diagnostics_channel

[GregoryDi]

What version of Bun is running?

1.3.13+bf2e2cecf

What platform is your computer?

Darwin 25.3.0 arm64 arm

What steps can reproduce the bug?

Problem

node:http server does not publish to HTTP server diagnostics_channel channels

Description

Bun implements the node:diagnostics_channel module, but its node:http
server does not publish to the standard Node.js HTTP server diagnostic channels.
This silently breaks any observability library that relies on these channels
for instrumentation (metrics, tracing, APM).

Note: HTTP client-side channels are being worked on in #24375. This issue
specifically tracks the missing server-side channels.

What is the expected behavior?

Node.js instruments its HTTP server internally by publishing to named
diagnostic channels at key points in the request/response lifecycle. This allows
libraries to subscribe and collect metrics or traces without wrapping or patching
any code.

HTTP Server channels

Channel	When
http.server.request.start	Server receives a request
http.server.response.created	Server creates a response object
http.server.response.finish	Server finishes sending a response

What do you see instead?

Subscribers to all of the above channels are never called. The diagnostics_channel
API itself works (subscribe/publish/channel), but node:http server never publishes
to any of these channels.

Additional information

Impact
Any observability library using diagnostics_channel for HTTP server instrumentation
does not work on Bun. Notable examples:

• OpenTelemetry Node.js HTTP instrumentation
• Any Prometheus HTTP metrics library following the Node.js diagnostics_channel spec
  Notes

I could not find any mentions of these channel names in the Bun codebase.

[robobun]

✅ Reproduced on 1.3.13. Fix in #29588 — publishes http.server.response.created, http.server.request.start, http.server.response.finish with the Node-matching payloads and ordering. The dc.subscribe(name, cb) GC concern (subscriptions getting dropped when no channel reference is held) is a separate bug already being fixed in #26537, so this PR stays focused on the server-side publishes.