Avoid forking rootScopes for Reactor if current thread has NoOpScopes

[adinauer]

📜 Description

Avoid forking rootScopes for Reactor if current thread has NoOpScopes.

SentryReactorThreadLocalAccessor.getValue() invokes Sentry.getCurrentScopes() which will fork rootScopes if there is no instance of IScopes available (null or NoOpScopes).

We now check for existence of IScopes before invoking getCurrentScopes() in order to avoid the unnecessary overhead.

💡 Motivation and Context

Potential fix for #4762

💚 How did you test it?

📝 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

[adinauer]

An alternative to exposing this could be to have an overload of Sentry.getCurrentScopes() that could e.g. have a bool parameter to specify whether to fork rootScopes or just return NoOpScopes if there's nothing there yet.

[lcian]

Hmm yeah I would prefer this option, however for the purpose of the release I'm fine to go with this for now

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	313.63 ms	353.94 ms	40.31 ms
Size	1.58 MiB	2.12 MiB	555.28 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
806307f	357.85 ms	424.64 ms	66.79 ms
ee747ae	554.98 ms	611.50 ms	56.52 ms
17a0955	372.53 ms	446.70 ms	74.17 ms
2124a46	319.19 ms	415.04 ms	95.85 ms
9fbb112	404.51 ms	475.65 ms	71.14 ms
b6702b0	395.86 ms	409.98 ms	14.12 ms
ee747ae	357.79 ms	421.84 ms	64.05 ms
27d7cf8	314.17 ms	347.00 ms	32.83 ms
9fbb112	361.43 ms	427.57 ms	66.14 ms
96449e8	361.30 ms	423.39 ms	62.09 ms

App size

Revision	Plain	With Sentry	Diff
806307f	1.58 MiB	2.10 MiB	533.42 KiB
ee747ae	1.58 MiB	2.10 MiB	530.95 KiB
17a0955	1.58 MiB	2.10 MiB	533.20 KiB
2124a46	1.58 MiB	2.12 MiB	551.51 KiB
9fbb112	1.58 MiB	2.11 MiB	539.18 KiB
b6702b0	1.58 MiB	2.12 MiB	551.79 KiB
ee747ae	1.58 MiB	2.10 MiB	530.95 KiB
27d7cf8	1.58 MiB	2.12 MiB	549.42 KiB
9fbb112	1.58 MiB	2.11 MiB	539.18 KiB
96449e8	1.58 MiB	2.11 MiB	539.35 KiB

[lcian]

Hmm yeah I would prefer this option, however for the purpose of the release I'm fine to go with this for now