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	14.01 s	14.00 s	[-0.7%; +0.9%] (no difference)
startup:insecure-bank:tracing:Agent	12.90 s	13.06 s	[-1.9%; -0.4%] (maybe better)
startup:petclinic:appsec:Agent	16.93 s	16.84 s	[-0.4%; +1.5%] (no difference)
startup:petclinic:iast:Agent	16.81 s	16.97 s	[-1.6%; -0.3%] (maybe better)
startup:petclinic:profiling:Agent	16.61 s	16.74 s	[-1.7%; +0.2%] (no difference)
startup:petclinic:sca:Agent	16.93 s	16.65 s	[+0.8%; +2.7%] (maybe worse)
startup:petclinic:tracing:Agent	16.05 s	16.23 s	[-2.0%; -0.2%] (maybe better)

Commit: 5fcbf2be · 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.