RUM-18174: Fix long task duration computation

[satween]

What does this PR do?

Fixes long task duration computation in MainLooperLongTaskStrategy and reduce hot method impact of the SDK.

The duration bug. startUptimeNs defaulted to 0L and was never reset after a dispatch completed. Any <<<<< Finished to that had no matching >>>>> Dispatching to — the first one after register(), or a repeated one for a dispatch already accounted for — computed now - 0, i.e. the entire device elapsed time, and reported it as a long task. On a device up for hours that surfaces as a multi-hour long task attached to whatever the main thread happened to be doing.

Dispatch state is republished per registration. register() installs a fresh DispatcherState behind a @Volatile field, so a strategy replaced while the main thread sits between a dispatch and its finish can no longer pair a start from before the swap with a finish from after it.

CompositePrinter cleanup.

• The main Looper message-logging printer is now uninstalled when the last strategy unregisters, so Looper.loop() stops building a log string for every message it dispatches once the SDK is stopped.

MainLooperLongTaskStrategy refactor .

• println executes on the ui thread. So object allocations and thread synchronization has been moved into other methods of the MainLooperLongTaskStrategy.

Motivation

RUM-18174 — long tasks were being reported with durations spanning the device uptime instead of the actual dispatch.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[Copilot]

Pull request overview

Fixes incorrect main-looper long-task durations and improves shared printer lifecycle and performance.

Changes:

• Resets dispatch state safely and ignores unmatched finish messages.
• Uses an identity-based, allocation-free printer registry.
• Expands lifecycle, duration, and concurrency tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
MainLooperLongTaskStrategy.kt	Refactors duration tracking and printer registration.
MainLooperLongTaskStrategyTest.kt	Adds duration, lifecycle, and race tests.
detekt_custom_safe_calls_third_party.yml	Allows Array.isEmpty().

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[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 85.37%
• Overall Coverage: 71.79% (+0.00%)

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[chatgpt-codex-connector]

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