[QA] Move NDK scope sync to background thread

[markushi]

📜 Description

Utilizes our ExecutorService to perform NDK scope sync (and it's JSON serialization) on a background thread.
This will cause an async scope sync, meaning if e.g. .setUser() returns, the value is not visible on the NDK side right away. The upside is faster execution.

If we see there's demand for an in-sync solution, we can introduce a flag later.

Motivation

Closes #3046

💚 How did you test it?

Extended tests

📝 Checklist

• I reviewed the submitted code.
• 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.
• 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

[github-actions]

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

Generated by 🚫 dangerJS against b3f16f7

[romtsn]

LGTM! Just thinking if we should introduce an ndk-specific executor here? Our default executor does too many things already 😅

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	432.26 ms	490.80 ms	58.54 ms
Size	1.70 MiB	2.35 MiB	667.90 KiB

Previous results on branch: feat/async-ndk-scope-sync

Startup times

Revision	Plain	With Sentry	Diff
3a599c8	662.49 ms	748.14 ms	85.65 ms
4139c9c	425.58 ms	460.88 ms	35.29 ms
57a3722	394.68 ms	462.96 ms	68.28 ms
d28a94e	411.56 ms	428.00 ms	16.44 ms

App size

Revision	Plain	With Sentry	Diff
3a599c8	1.70 MiB	2.35 MiB	661.36 KiB
4139c9c	1.70 MiB	2.35 MiB	661.36 KiB
57a3722	1.70 MiB	2.35 MiB	667.55 KiB
d28a94e	1.70 MiB	2.35 MiB	661.36 KiB