Fix faulty span.frame_delay calculation for early app start spans

[markushi]

📜 Description

The return value of frameMetricsCollector.getLastKnownFrameStartTimeNanos() was ignored, thus creating large frame delay values.

I also moved data collection post initial tracer.finish, ensuring a finish timestamp is set and spans / txns are already trimmed. This is especially useful for idle ui.load transactions, as otherwise the frame delay will be longer than the txn duration.

💡 Motivation and Context

💚 How did you test it?

📝 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	378.62 ms	453.98 ms	75.36 ms
Size	1.70 MiB	2.28 MiB	592.12 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
7ca9895	364.31 ms	460.46 ms	96.15 ms
bf82eb3	423.76 ms	506.45 ms	82.69 ms
d429384	397.33 ms	457.69 ms	60.36 ms
f5e1b97	362.53 ms	429.31 ms	66.78 ms
c554ca2	368.52 ms	430.74 ms	62.22 ms
9119d59	407.12 ms	509.64 ms	102.52 ms
a33b076	381.94 ms	459.64 ms	77.71 ms
93a76ca	397.30 ms	455.16 ms	57.87 ms
283d83e	348.44 ms	392.06 ms	43.62 ms
9e57f46	368.94 ms	410.50 ms	41.56 ms

App size

Revision	Plain	With Sentry	Diff
7ca9895	1.72 MiB	2.29 MiB	576.51 KiB
bf82eb3	1.70 MiB	2.28 MiB	587.99 KiB
d429384	1.72 MiB	2.27 MiB	558.42 KiB
f5e1b97	1.70 MiB	2.28 MiB	592.00 KiB
c554ca2	1.70 MiB	2.27 MiB	582.25 KiB
9119d59	1.70 MiB	2.27 MiB	583.84 KiB
a33b076	1.70 MiB	2.28 MiB	592.32 KiB
93a76ca	1.72 MiB	2.29 MiB	576.75 KiB
283d83e	1.72 MiB	2.29 MiB	577.69 KiB
9e57f46	1.70 MiB	2.28 MiB	592.08 KiB

Previous results on branch: fix/huge-frame-delay

Startup times

Revision	Plain	With Sentry	Diff
ab36940	378.21 ms	454.76 ms	76.55 ms

App size

Revision	Plain	With Sentry	Diff
ab36940	1.70 MiB	2.28 MiB	592.12 KiB

[stefanosiano]

nice!