chore: Add tracking for feature flags

[denrase]

#skip-changelog

📜 Description

Track runtime use of the manual feature flag APIs by adding featureFlags to sdk.features after the API is used.

Runtime-discovered feature flag usage is stored internally and thread-safely on the active SDK options, then merged with the existing option-derived features when SDK metadata is built.

💡 Motivation and Context

We want internal telemetry showing actual feature flag API adoption, matching the behavior in sentry-flutter. Inferring this at SDK initialization is not possible because feature flags are enabled through runtime API usage.

Closes #8594

💚 How did you test it?

• Added tests for storage, concurrency, SDK metadata generation, and the SDK/Hub feature flag entry points.
• Manually used Add Scope Flag in the iOS Swift sample, captured an event, and confirmed featureFlags appears in the event's sdk.features JSON.
• Link to Sentry: https://sentry-sdks.sentry.io/issues/6607086585/events/latest/?project=5428557&query=is%3Aunresolved&referrer=latest-event

📝 Checklist

• 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.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.
• If I added a new public API, I also added it to the SentryObjC wrapper.

[sentry]

📲 Install Builds

iOS

🔗 App Name	App ID	Version	Configuration
SDK-Size	io.sentry.sample.SDK-Size	9.25.0 (1)	Release

⚙️ sentry-cocoa Build Distribution Settings

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1211.74 ms	1255.93 ms	44.19 ms
Size	24.14 KiB	1.27 MiB	1.25 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
6beeea8	1220.50 ms	1253.93 ms	33.43 ms
5a9c804	1220.29 ms	1255.17 ms	34.88 ms
2ce4807	1220.52 ms	1254.02 ms	33.50 ms
b69e199	1210.45 ms	1251.13 ms	40.68 ms
35901c8	1217.02 ms	1259.13 ms	42.11 ms
3b7d81f	1220.53 ms	1239.06 ms	18.53 ms
871ce4d	1223.43 ms	1257.17 ms	33.75 ms
a879c92	1229.37 ms	1262.33 ms	32.97 ms
fc5cefc	1222.44 ms	1254.20 ms	31.77 ms
56dbf49	1236.41 ms	1261.31 ms	24.89 ms

App size

Revision	Plain	With Sentry	Diff
6beeea8	24.14 KiB	1.23 MiB	1.21 MiB
5a9c804	24.14 KiB	1.15 MiB	1.13 MiB
2ce4807	24.14 KiB	1.23 MiB	1.20 MiB
b69e199	24.14 KiB	1.24 MiB	1.22 MiB
35901c8	24.14 KiB	1.24 MiB	1.21 MiB
3b7d81f	24.14 KiB	1.22 MiB	1.20 MiB
871ce4d	24.14 KiB	1.22 MiB	1.20 MiB
a879c92	24.14 KiB	1.25 MiB	1.23 MiB
fc5cefc	24.14 KiB	1.17 MiB	1.14 MiB
56dbf49	24.14 KiB	1.27 MiB	1.25 MiB

Previous results on branch: chore/add-tracking-for-feature-flags

Startup times

Revision	Plain	With Sentry	Diff
bbe0e31	1227.21 ms	1260.16 ms	32.95 ms
af59095	1215.42 ms	1254.00 ms	38.58 ms

App size

Revision	Plain	With Sentry	Diff
bbe0e31	24.14 KiB	1.27 MiB	1.24 MiB
af59095	24.14 KiB	1.27 MiB	1.25 MiB

[itaybre]

This seems a bit over engineered, at this moment I believe a simple boolean flag would be simpler and if we end up with other features like this we can build the set logic

[denrase]

@itaybre Thought I add something generic as we track multiple runtime values in flutter and it's easy to query this data, but we can also do it simpy and then expand if needed.

[philippsuess]

I agree with @itaybre. We already sent this information with the events. We pull the features list from the scope. I tried to get that info in Hex, but we don't index that info yet.

@itaybre I think we should talk to the data team and ask them to index this, so we see how many projects and orgs use this. Maybe also numbers on how many events have feature flags and how many would be useful, but mostly how many orgs and projects. As I'm on PTO soon, @itaybre or @denrase, could you maybe talk to the data team so we get this info?

Then we could close this PR.

[denrase]

@philipphofmann Will do, putting this in draft/blocked for now until we have an aswer.