[WIP] add pre-signal state check for wallclock

[kaahos]

What does this PR do?:

Adds a pre-signal check to the wall-clock timer loop that reads the OS thread state before sending a signal. When a thread is in SLEEPING state, the signal is skipped.

Motivation:

The wall-clock profiler sends a signal to every tracked thread at ~1ms intervals. For threads blocked, this generates up to 1000 signals/second that all produce the same stack, and the profiler learns nothing new from repeated samples. At large scale, we observe undesirable effects like signal storms, cache thrashing or sample distortion. Skipping those signals reduces unnecessary overhead without losing meaningful profiling data.

Additional Notes:

How to test the change?:

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.
• JIRA: [JIRA-14354]

Unsure? Have a question? Request a review!

[dd-octo-sts]

CI Test Results

Run: #25169296748 | Commit: cdbf156 | Duration: 28m 39s (longest job)

✅ All 32 test jobs passed

Status Overview

JDK	glibc-aarch64/debug	glibc-amd64/debug	musl-aarch64/debug	musl-amd64/debug
8	-	✅	-	-
8-ibm	-	✅	-	-
8-j9	✅	✅	-	-
8-librca	-	-	✅	✅
8-orcl	-	✅	-	-
11	-	✅	-	-
11-j9	✅	✅	-	-
11-librca	-	-	✅	✅
17	✅	✅	-	-
17-graal	✅	✅	-	-
17-j9	✅	✅	-	-
17-librca	-	-	✅	✅
21	✅	✅	-	-
21-graal	✅	✅	-	-
21-librca	-	-	✅	✅
25	✅	✅	-	-
25-graal	✅	✅	-	-
25-librca	-	-	✅	✅

Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled

Summary: Total: 32 | Passed: 32 | Failed: 0

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Updated: 2026-04-30 14:40:16 UTC