feat(profiling): internal metrics for overhead improvements

[realFlowControl]

Important

This PR is not against master, but against levi/stack_walk_metric in #3616

Description

A few improvements to the CPU time tracking for background threads:

• Moved update_background_cpu_time() to just before exporter.build() so that profile serialization time is included in the metric for the current exported profile. Note: metadata generation, exporter building, and HTTP request time will still be attributed to the next profile period (left a comment in the code about that as well)
• Added tracking for ddprof_time thread
• Split the single background_threads_cpu_time_ns counter into two metrics, ddprof_time_cpu_time_ns for the ddprof_time thread and ddprof_upload_cpu_time_ns for the ddprof_upload thread

I did those changes in three separate commits (in the order above).

{
  "ddprof_upload_cpu_time_ns": 894625,
  "libdatadog_version": "1.0.0",
  "stack_walk_cpu_time_ns": 0,
  "stack_walk_count": 0,
  "ddprof_time_cpu_time_ns": 8158083
}

vs.

{
  "libdatadog_version": "1.0.0",
  "stack_walk_cpu_time_ns": 0,
  "stack_walk_count": 0,
  "background_threads_cpu_time_ns": 28375
}

.. on the first profile received.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[datadog-official]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 1024 Tests failed

    testSearchPhpBinaries from integration.DDTrace\Tests\Integration\PHPInstallerTest (Fix with Cursor)

    testSimplePushAndProcess from laravel-58-test.DDTrace\Tests\Integrations\Laravel\V5_8\QueueTest (Fix with Cursor)

testSimplePushAndProcess from laravel-8x-test.DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest (Datadog) (Fix with Cursor)

DDTrace\Tests\Integrations\Laravel\V8_x\QueueTest::testSimplePushAndProcess
Test code or tested code printed unexpected output: spanLinksTraceId: 698332100000000085602b6eeb041df1
tid: 6983321000000000
hexProcessTraceId: 85602b6eeb041df1
hexProcessSpanId: 73e46101f50beaa6
processTraceId: 9610729360197950961
processSpanId: 8350906270085802662

View all

ℹ️ Info

❄️ No new flaky tests detected

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