feat(micrometer): [Micrometer 3] Add function timer polling

[adinauer]

PR Stack (Micrometer)

• feat(micrometer): Add Micrometer metrics integration #6084
• feat(micrometer): [Micrometer 1] Add active meters #6085
• feat(micrometer): [Micrometer 2] Add passive meter polling #6114
• feat(micrometer): [Micrometer 3] Add function timer polling #6115
• feat(micrometer): [Micrometer 4] Add Spring Boot integration #6116

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📜 Description

Add passive polling for Micrometer FunctionTimer meters.

Each function timer emits positive changes in its cumulative count and total time as <name>.count and <name>.total_time Sentry counters. The implementation establishes an initial baseline, handles source resets, skips invalid values, and resets its state when the meter is removed.

💡 Motivation and Context

Micrometer function timers expose cumulative count and total-time callbacks. Those values cannot reconstruct the original observations needed for a Sentry distribution or a meaningful per-instance mean, so this PR preserves their representable semantics as independent counter deltas.

Keeping this mapping separate makes the semantic tradeoff explicit and reviewable.

💚 How did you test it?

./gradlew spotlessApply apiDump
./gradlew :sentry-micrometer:check

Tests cover baselines, positive deltas, count-only and time-only changes, resets, non-finite and negative values, meter removal, units, tags, and callback failures.

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.

🔮 Next steps

Add opt-in Spring Boot 2, 3, and 4 integration in the final stack PR.

#skip-changelog

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

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SDK Size	io.sentry.tests.size	8.56.0 (1)	release

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