Fix metrics-api JaCoCo coverage gate

[dougqh]

What Does This Do

• products/metrics/metrics-api never opted into the excludedClassesCoverage convention used by sibling modules, so the repo-wide 0.9 minimum instruction/branch coverage rule failed for every NoOp* class as soon as CI ran this module's full check task (module-scoped CI hadn't run a full check here in a while).
• Excludes the true no-op classes (NoOpCounter, NoOpHistogram, NoOpHistogramsFactory, NoOpMonitoring, NoOpRecording, NoOpStatsDClient) and the pure-interface Monitoring.
• Adds the module's first src/test tree with real unit tests for the classes that have actual untested logic: Histograms (registration + static factory dispatch), StatsDClientManager (default 5-arg overload delegating to the 6-arg one), Recording (close() delegates to stop()), and a small StatsDClient test to clear its default recordEvent method.

Motivation

Unrelated to any in-flight feature work — this is a pre-existing coverage gap surfaced while working on #12351, which switched metrics-api's build.gradle.kts to the dd-trace-java.module.internal-api plugin and newly exposed the module to this gate. Kept as its own PR rather than folded into #12351, since the two are independent and shouldn't be reviewed together.

Additional Notes

• Test plan:
  • ./gradlew :products:metrics:metrics-api:test
  • ./gradlew :products:metrics:metrics-api:jacocoTestCoverageVerification
  • ./gradlew :products:metrics:metrics-api:check

Contributor Checklist

• Format the title according to the contribution guidelines
• Assign the type: and (comp: or inst:) labels in addition to any other useful labels
• Avoid using close, fix, or any linking keywords when referencing an issue
• Update the CODEOWNERS file on source file addition, migration, or deletion (n/a — no new top-level source areas)
• Update public documentation with any new configuration flags or behaviors (n/a — no config/behavior change)
• Once approved, use merge queue to merge the PR

Jira ticket: none — pre-existing gap found incidentally, not tracked separately

🤖 Generated with Claude Code

[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	14.79 s	14.68 s	[-0.2%; +1.7%] (no difference)
startup:insecure-bank:tracing:Agent	13.62 s	13.70 s	[-1.3%; +0.2%] (no difference)
startup:petclinic:appsec:Agent	17.60 s	17.34 s	[+0.6%; +2.4%] (maybe worse)
startup:petclinic:iast:Agent	17.49 s	17.62 s	[-1.6%; +0.1%] (no difference)
startup:petclinic:profiling:Agent	17.38 s	17.48 s	[-1.6%; +0.4%] (no difference)
startup:petclinic:sca:Agent	16.88 s	17.49 s	[-7.7%; +0.7%] (no difference)
startup:petclinic:tracing:Agent	16.56 s	16.64 s	[-1.5%; +0.4%] (no difference)

Commit: be114a1c · 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.

[datadog-datadog-us1-prod]

More details

The coverage exclusions match the no-op and interface classes. The new tests cover the remaining default and factory behavior.

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