runtime,runtime/pprof: clean up goroutine leak profile writing

[VladSaiocUber]

Cleaned up goroutine leak profile extraction:

• removed the acquisition of goroutineProfile semaphore
• inlined the call to saveg when recording stacks instead of using
  doRecordGoroutineProfile, which had side-effects over
  goroutineProfile fields.

Added regression tests for goroutine leak profiling frontend for binary
and debug=1 profile formats.
Added stress tests for concurrent goroutine and goroutine leak profile requests.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Georgian-Vlad Saioc:

Patch Set 3:

(1 comment)

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Message from Georgian-Vlad Saioc:

Patch Set 3:

(1 comment)

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Message from t hepudds:

Patch Set 3: Commit-Queue+1

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Message from Go LUCI:

Patch Set 3:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-10-27T11:25:05Z","revision":"b56ebcfe8ea10abbbd4dc11673785d168bf8f191"}

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Message from t hepudds:

Patch Set 3: -Commit-Queue

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Message from Go LUCI:

Patch Set 3:

This CL has failed the run. Reason:

Tryjob golang/try/gotip-linux-386 has failed with summary (view all results):

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• go on master (change 714580)

To reproduce, try gomote repro 8699859655765379761.

Additional links for debugging:

• go tool dist test -json output [shard 1]

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Message from Go LUCI:

Patch Set 3: LUCI-TryBot-Result-1

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