fix: reportFullyDisplayed data race

[philipphofmann]

📜 Description

Fix a data race when calling reportFullyDisplayed from a background thread by synchronizing the call to the main queue.

💡 Motivation and Context

This came up when enabling the thread sanitizer for the iOS-Swift sample app and navigating to the LoremIpsum screen.

💚 How did you test it?

Unit tests and thread sanitizer in the iOS-Swift sample app.

📝 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

All modified and coverable lines are covered by tests ✅

Project coverage is 90.802%. Comparing base (9537eaf) to head (f503ecc).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3926       +/-   ##
=============================================
- Coverage   90.846%   90.802%   -0.045%     
=============================================
  Files          593       592        -1     
  Lines        46028     45949       -79     
  Branches     16432     16363       -69     
=============================================
- Hits         41815     41723       -92     
- Misses        4034      4045       +11     
- Partials       179       181        +2     

Files	Coverage Δ
Sources/Sentry/SentryTimeToDisplayTracker.m	100.000% <100.000%> (ø)
.../Sentry/SentryUIViewControllerPerformanceTracker.m	99.024% <100.000%> (+0.009%)	⬆️
...iewController/SentryTimeToDisplayTrackerTest.swift	100.000% <100.000%> (ø)
Tests/SentryTests/SentryHubTests.swift	98.850% <100.000%> (ø)

... and 19 files with indirect coverage changes

---

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1229.15 ms	1251.33 ms	22.18 ms
Size	21.58 KiB	617.00 KiB	595.42 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
f74904f	1229.02 ms	1244.91 ms	15.89 ms
591a01b	1242.69 ms	1259.98 ms	17.29 ms
60dd0f5	1212.24 ms	1240.82 ms	28.58 ms
e1cd9e9	1190.64 ms	1221.90 ms	31.26 ms
5f8ee7a	1249.48 ms	1252.20 ms	2.72 ms
69d8759	1229.88 ms	1240.45 ms	10.57 ms
e89dc54	1207.86 ms	1218.27 ms	10.41 ms
f801098	1225.41 ms	1237.45 ms	12.04 ms
c0b4b71	1218.16 ms	1251.28 ms	33.12 ms
bbcbaff	1216.82 ms	1242.34 ms	25.52 ms

App size

Revision	Plain	With Sentry	Diff
f74904f	21.58 KiB	418.71 KiB	397.12 KiB
591a01b	22.84 KiB	401.67 KiB	378.83 KiB
60dd0f5	20.76 KiB	393.37 KiB	372.61 KiB
e1cd9e9	22.85 KiB	412.95 KiB	390.10 KiB
5f8ee7a	22.85 KiB	411.93 KiB	389.08 KiB
69d8759	20.76 KiB	393.05 KiB	372.29 KiB
e89dc54	22.85 KiB	412.60 KiB	389.75 KiB
f801098	21.58 KiB	614.71 KiB	593.13 KiB
c0b4b71	20.76 KiB	430.98 KiB	410.22 KiB
bbcbaff	22.85 KiB	414.09 KiB	391.24 KiB