Implement opt-in BEAM runtime metrics

[dingsdax]

The BEAM runtime collector identified in ELIXIR-45 was merged on September 22, 2026. This issue records the completed implementation; publication and release-readiness checks remain tracked by the project.

• feat(metrics): add opt-in BEAM runtime metrics collector #1188: opt-in collector, memory gauges, configuration, and lifecycle wiring.
• feat(metrics): report run queue depth in runtime metrics #1212: total, CPU, and I/O run-queue gauges.
• feat(metrics): report process, atom and port counts in runtime metrics #1213: process, atom, and port counts, limits, and utilization ratios; limits are omitted on older pollers.
• feat(metrics): report scheduler utilization in runtime metrics #1189: scheduler utilization from successive samples.
• Implemented in lib/sentry/metrics/runtime.ex, with configuration in lib/sentry/config.ex, API documentation in lib/sentry/metrics.ex, and tests in test/sentry/metrics/runtime_test.exs.
• Runtime collection and version attributes are disabled by default. Configuration marks availability as 14.0.0; latest published GitHub release checked on September 25, 2026 was 13.5.1.

Action taken on behalf of Johannes Daxboeck.

[linear-code]

ELIXIR-77