Backpressure

[jamescrosswell]

Resolves #2410

• Backpressure Management #2410

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Note

Introduces optional automatic backpressure handling that dynamically downsamples events/traces based on queue overflows and server rate limits, wired through worker, transport, hub, and client with full test coverage.

• Feature: Backpressure handling
  • Add BackpressureMonitor and new option SentryOptions.EnableBackpressureHandling (incl. config binding) to automatically reduce SampleRate/TracesSampleRate when under pressure.
  • Record signals from BackgroundWorker (queue overflows) and HttpTransportBase (rate-limit headers) to drive downsampling; mark discards with DiscardReason.Backpressure.
  • Apply downsample factor in Hub.StartTransaction and SentryClient.DoSendEvent; dispose monitor on hub shutdown.
• Plumbing
  • Thread monitor through SdkComposer, BackgroundWorker, LazyHttpTransport/HttpTransport, and HttpTransportBase (constructor changes).
  • Minor benchmark/test adjustments for updated signatures.
• Tests & API
  • Add comprehensive unit tests for backpressure behavior; update public API approvals to include EnableBackpressureHandling.
• Docs
  • Update CHANGELOG.md with the new feature.

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