refactor(propagation): Parse OpenTelemetry tracestate member

[MilanGarnier]

What Does This Do

Refactors W3C tracestate handling so the OpenTelemetry ot member is
represented separately while its value remains opaque.

• Extracts and re-emits the raw ot member.
• Preserves its inherited position when rebuilding tracestate.
• Does not interpret rv or th or connect the member to sampling.

Motivation

Isolate the tracestate parsing foundation from the consistent-sampling
behavior added by the follow-up PR.

Additional Notes

This is the first PR in a two-PR stack. The sampling behavior follows in
#12397.

Validation:

• :dd-trace-core:compileJava
• :dd-trace-core:spotlessCheck
• git diff --check

Contributor Checklist

• Format the title according to the contribution guidelines.
• Assign the required type: and comp: labels.
• Keep sampling behavior and tests in the follow-up PR.

Jira ticket: APMAPI-2171

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.94 s	13.85 s	[-0.1%; +1.4%] (no difference)
startup:insecure-bank:tracing:Agent	12.81 s	12.87 s	[-1.2%; +0.3%] (no difference)
startup:petclinic:appsec:Agent	17.02 s	16.92 s	[-0.3%; +1.4%] (no difference)
startup:petclinic:iast:Agent	16.90 s	17.05 s	[-1.6%; -0.2%] (maybe better)
startup:petclinic:profiling:Agent	16.73 s	16.01 s	[+0.3%; +8.8%] (maybe worse)
startup:petclinic:sca:Agent	16.88 s	16.70 s	[+0.0%; +2.1%] (maybe worse)
startup:petclinic:tracing:Agent	16.01 s	16.23 s	[-2.3%; -0.4%] (maybe better)

Commit: 25dcc81f · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.