feat: Add async event processing

[adinauer]

📜 Description

Adds opt-in async event processing for SDK event capture paths.

This introduces EventProcessor.processAsync(...) overloads for events, transactions, replay events, log events, and metrics events. When enableAsyncProcessing is enabled, late processing callbacks and before-send execution run through a dedicated bounded single-thread queue so capture calls can return after async work is accepted. The queue uses maxQueueSize, reports queue_overflow on rejection, and returns SentryId.EMPTY_ID for ID-returning captures that cannot be queued.

Also adds the external option key enable-async-processing, flush/close draining behavior for async work, API updates, and a design note covering telemetry processor compatibility.

💡 Motivation and Context

Some event processors and before-send callbacks can be expensive or user-defined. Running them on the capture caller thread can increase application latency. This feature keeps the existing synchronous behavior by default while allowing users to opt in to moving the late processing stage off the caller thread.

💚 How did you test it?

• ./gradlew spotlessApply apiDump
• ./gradlew :sentry:test --tests 'io.sentry.SentryClientTest' --tests 'io.sentry.SentryOptionsTest' --tests 'io.sentry.ExternalOptionsTest'
• Close-specific regression tests

📝 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.

🔮 Next steps

Consider follow-up work to migrate selected SDK-owned expensive processors to processAsync(...) where doing so does not capture stale request, thread-local, or UI state.

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against d129f49

[sentry]

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.43.2 (1)	release

⚙️ sentry-android Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	306.63 ms	357.28 ms	50.65 ms
Size	0 B	0 B	0 B

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
a416a65	333.78 ms	410.37 ms	76.59 ms
d15471f	304.55 ms	408.43 ms	103.87 ms
ca6b6d8	380.45 ms	460.38 ms	79.93 ms
c8125f3	397.65 ms	485.14 ms	87.49 ms
b936425	302.69 ms	372.86 ms	70.17 ms
ed33deb	334.19 ms	362.30 ms	28.11 ms
cf708bd	408.35 ms	458.98 ms	50.63 ms
eb95ded	317.51 ms	369.08 ms	51.57 ms
a5ab36f	320.47 ms	389.77 ms	69.30 ms
80fd6ad	321.06 ms	375.79 ms	54.73 ms

App size

Revision	Plain	With Sentry	Diff
a416a65	1.58 MiB	2.12 MiB	555.26 KiB
d15471f	1.58 MiB	2.13 MiB	559.54 KiB
ca6b6d8	0 B	0 B	0 B
c8125f3	1.58 MiB	2.10 MiB	532.32 KiB
b936425	0 B	0 B	0 B
ed33deb	1.58 MiB	2.13 MiB	559.52 KiB
cf708bd	1.58 MiB	2.11 MiB	539.71 KiB
eb95ded	0 B	0 B	0 B
a5ab36f	1.58 MiB	2.12 MiB	555.26 KiB
80fd6ad	0 B	0 B	0 B