feat: add trace_id pprof label

[marcsanmi]

Summary

Attaches a trace_id pprof label (32-char W3C hex) to profile samples, enabling traces↔profiles correlation by trace ID server-side. Emitted unconditionally, matching the Go/Python SDKs; span_id and pyroscope.profile.id behavior is unchanged.

Uses the ProfilerApi.setTraceId(String) / clearTraceId() methods added in grafana/pyroscope-java#313 (the otel-extension path). The library processor calls the native AsyncProfiler.setTraceId(hi, lo) directly, with an allocation-free hex parser.

Requires pyroscope-java >= 2.6.0 (now on Maven Central).

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[simonswine]

Needs rebase to pass the tests, but in general looks good to me

[korniltsev-grafanista]

wait, why does querying by trace_id series label work on your screenshot? I thought we removed trace_id label same way as span_id

[marcsanmi]

why does querying by trace_id series label work on your screenshot?

Yes, this was the first test I did on all the SDKs before the fix I did on Pyroscope.