fix: Rarely reporting too long frame delays

[philipphofmann]

📜 Description

Fix a race condition in the SentryFramesTracker and SentryDelayedFramesTracker that sometimes leads to frame delay durations longer than the queried interval of start and end time. This is fixed by moving the previousFrameSystemTimestamp down to the SentryDelayedFramesTracker so we can adequately synchronize it without acquiring extra locks on the main thread.

💡 Motivation and Context

Came up while working on GH-3492.

💚 How did you test it?

Unit test.

📝 Checklist

You have to check all boxes before merging:

• 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

[codecov]

Codecov Report

Attention: Patch coverage is 97.22222% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.547%. Comparing base (464117d) to head (dcbe5eb).

Files	Patch %	Lines
Sources/Sentry/SentryDelayedFramesTracker.m	90.909%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4278       +/-   ##
=============================================
- Coverage   91.612%   91.547%   -0.065%     
=============================================
  Files          616       615        -1     
  Lines        50000     49939       -61     
  Branches     18091     18012       -79     
=============================================
- Hits         45806     45718       -88     
- Misses        4103      4128       +25     
- Partials        91        93        +2     

Files	Coverage Δ
SentryTestUtils/TestDisplayLinkWrapper.swift	95.890% <100.000%> (+0.176%)	⬆️
Sources/Sentry/SentryFramesTracker.m	99.354% <100.000%> (+0.653%)	⬆️
...ance/FramesTracking/SentryFramesTrackerTests.swift	99.551% <100.000%> (+0.018%)	⬆️
Sources/Sentry/SentryDelayedFramesTracker.m	99.009% <90.909%> (-0.991%)	⬇️

... and 24 files with indirect coverage changes

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1231.16 ms	1245.45 ms	14.28 ms
Size	21.58 KiB	705.65 KiB	684.07 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
f1c36e0	1215.18 ms	1223.62 ms	8.43 ms
939cd63	1222.53 ms	1250.76 ms	28.23 ms
2a894d5	1202.07 ms	1227.66 ms	25.59 ms
65f104b	1229.87 ms	1247.69 ms	17.82 ms
46bb3fe	1221.53 ms	1234.24 ms	12.71 ms
aeec206	1229.27 ms	1253.70 ms	24.43 ms
31ac438	1244.29 ms	1264.06 ms	19.78 ms
10ee2ce	1250.90 ms	1258.57 ms	7.67 ms
eb41178	1228.06 ms	1248.37 ms	20.31 ms
25bcc50	1240.47 ms	1254.70 ms	14.23 ms

App size

Revision	Plain	With Sentry	Diff
f1c36e0	21.58 KiB	670.40 KiB	648.81 KiB
939cd63	21.58 KiB	424.35 KiB	402.76 KiB
2a894d5	21.58 KiB	414.57 KiB	392.99 KiB
65f104b	21.58 KiB	625.82 KiB	604.24 KiB
46bb3fe	21.58 KiB	542.19 KiB	520.61 KiB
aeec206	20.76 KiB	434.88 KiB	414.12 KiB
31ac438	20.76 KiB	393.36 KiB	372.60 KiB
10ee2ce	20.76 KiB	427.77 KiB	407.00 KiB
eb41178	21.58 KiB	544.86 KiB	523.28 KiB
25bcc50	20.76 KiB	427.22 KiB	406.46 KiB

Previous results on branch: fix/too-long-frame-delays

Startup times

Revision	Plain	With Sentry	Diff
f8d77f9	1227.02 ms	1250.57 ms	23.55 ms

App size

Revision	Plain	With Sentry	Diff
f8d77f9	21.58 KiB	705.65 KiB	684.07 KiB