feat(otlp): cache OpenTelemetry trace state in OTLP export

[MilanGarnier]

What Does This Do

Exports the full existing W3C tracestate through OTLP. When no full W3C tracestate exists, the JSON and protobuf exporters reuse a cached ot= member for every local span in the trace chunk.

Motivation

Preserves the existing OTLP tracestate contract while exporting locally generated OpenTelemetry sampling state without per-span ot= allocation.

Additional Notes

Validated with focused OTLP JSON/protobuf tests and :dd-trace-core:spotlessCheck.

Contributor Checklist

• Title and labels follow repository conventions
• Tests and formatting checks pass

Jira ticket: APMAPI-2172

[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	13.96 s	14.01 s	[-1.5%; +0.7%] (no difference)
startup:insecure-bank:tracing:Agent	12.92 s	13.02 s	[-1.5%; -0.0%] (maybe better)
startup:petclinic:appsec:Agent	17.53 s	17.34 s	[+0.1%; +2.1%] (maybe worse)
startup:petclinic:iast:Agent	16.72 s	17.50 s	[-8.5%; -0.3%] (maybe better)
startup:petclinic:profiling:Agent	17.19 s	16.64 s	[-1.1%; +7.7%] (no difference)
startup:petclinic:sca:Agent	17.50 s	17.46 s	[-0.6%; +1.2%] (no difference)
startup:petclinic:tracing:Agent	16.52 s	16.56 s	[-1.2%; +0.7%] (no difference)

Commit: 80b5a9ad · CI Pipeline · Benchmarking Platform UI

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