Fix wrong txn duration in case SDK init is deferred

[markushi]

📜 Description

Ensure the firstActivityCreated flag is also set when activities go to background.

💡 Motivation and Context

Fixes #3059

💚 How did you test it?

Manual testing + unit 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]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	407.82 ms	445.40 ms	37.58 ms
Size	1.72 MiB	2.27 MiB	558.22 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
4e260b3	378.73 ms	454.18 ms	75.45 ms
93a76ca	397.30 ms	455.16 ms	57.87 ms
0bd723b	412.52 ms	496.65 ms	84.13 ms
1f3652d	361.62 ms	424.76 ms	63.14 ms
86f0096	381.33 ms	476.58 ms	95.25 ms
bc4be3b	360.40 ms	435.04 ms	74.64 ms
b172d4e	412.60 ms	492.68 ms	80.08 ms
4e260b3	388.40 ms	468.98 ms	80.58 ms
b172d4e	352.92 ms	446.50 ms	93.58 ms
93a76ca	377.96 ms	447.52 ms	69.56 ms

App size

Revision	Plain	With Sentry	Diff
4e260b3	1.72 MiB	2.27 MiB	554.95 KiB
93a76ca	1.72 MiB	2.29 MiB	576.75 KiB
0bd723b	1.72 MiB	2.29 MiB	578.09 KiB
1f3652d	1.72 MiB	2.27 MiB	554.95 KiB
86f0096	1.72 MiB	2.29 MiB	576.50 KiB
bc4be3b	1.72 MiB	2.29 MiB	576.53 KiB
b172d4e	1.72 MiB	2.29 MiB	578.09 KiB
4e260b3	1.72 MiB	2.27 MiB	554.95 KiB
b172d4e	1.72 MiB	2.29 MiB	578.09 KiB
93a76ca	1.72 MiB	2.29 MiB	576.75 KiB

Previous results on branch: fix/txn-duration-on-late-sdk-init

Startup times

Revision	Plain	With Sentry	Diff
28ea623	381.74 ms	445.94 ms	64.20 ms
6f485f5	372.29 ms	417.70 ms	45.41 ms

App size

Revision	Plain	With Sentry	Diff
28ea623	1.72 MiB	2.27 MiB	554.97 KiB
6f485f5	1.72 MiB	2.27 MiB	554.97 KiB

[stefanosiano]

yeah, this should work 👍