chore: Add integration tests for metrics

[tustanivsky]

Key changes:

• Add metric-capture test scenario to the sample app that emits counter, distribution and gauge metrics with a shared test_id attribute
• Add CppBeforeMetricHandler to the sample app that adds and removes attributes on metrics before they are sent
• Add metrics integration tests for Desktop (Windows/Linux) and Android that verify:
  • All three metric types arrive in Sentry with correct name, type, and value
  • BeforeMetricHandler correctly adds new attributes and removes existing ones
• Skip metrics tests on macOS since Apple platforms currently don't support custom metrics
• Bump app-runner to include Get-SentryMetrics, Get-SentryMetricsByAttribute, and Get-SentryTestMetric helpers that query the tracemetrics dataset
• Remove redundant BeforeMetricHandler unit tests

Depends on:

• feat: Add utilities to query metrics from Sentry app-runner#38

Related items:

• Add Metrics API support #1214
• Replace unit tests that rely on subsystem re-initialization with e2e integration tests #1225

#skip-changelog

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

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