fix: reportFullyDisplayed data race

[philipphofmann]

:scroll: Description

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

:bulb: Motivation and Context

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

:green_heart: How did you test it?

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

:pencil: Checklist

You have to check all boxes before merging:

• [x] I reviewed the submitted code.
• [x] I added tests to verify the changes.
• [x] No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• [x] I updated the docs if needed.
• [x] Review from the native team if needed.
• [x] No breaking change or entry added to the changelog.
• [x] No breaking change for hybrid SDKs or communicated to hybrid SDKs.

:crystal_ball: Next steps

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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%)	:arrow_up:
...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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Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 9537eaf...f503ecc. Read the comment docs.

[github-actions[bot]]

Performance metrics :rocket:

	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
f74904fa87218947c77c10540d685d25a43a1dd1	1229.02 ms	1244.91 ms	15.89 ms
591a01b3e320697e7cc86082284d786c359306e3	1242.69 ms	1259.98 ms	17.29 ms
60dd0f5656d961f9a9d604ceaf8dd5d99efd393d	1212.24 ms	1240.82 ms	28.58 ms
e1cd9e96643eb9563e7c09d6333b8ee67fca8798	1190.64 ms	1221.90 ms	31.26 ms
5f8ee7a3ef74bc6e32496015eb0cf13a539aedb8	1249.48 ms	1252.20 ms	2.72 ms
69d87595b411be6c93e72de62bc47457202fb72d	1229.88 ms	1240.45 ms	10.57 ms
e89dc54f3fd0c7ad010d9a6c7cb02ac178f3fc33	1207.86 ms	1218.27 ms	10.41 ms
f80109876fb5910e278957499d566bc708adffe1	1225.41 ms	1237.45 ms	12.04 ms
c0b4b714a9bc728c3452ce2627ea9b6c3275bb99	1218.16 ms	1251.28 ms	33.12 ms
bbcbaff4d524bd3af8e88f0f245b2e4256ffca3c	1216.82 ms	1242.34 ms	25.52 ms

App size

Revision	Plain	With Sentry	Diff
f74904fa87218947c77c10540d685d25a43a1dd1	21.58 KiB	418.71 KiB	397.12 KiB
591a01b3e320697e7cc86082284d786c359306e3	22.84 KiB	401.67 KiB	378.83 KiB
60dd0f5656d961f9a9d604ceaf8dd5d99efd393d	20.76 KiB	393.37 KiB	372.61 KiB
e1cd9e96643eb9563e7c09d6333b8ee67fca8798	22.85 KiB	412.95 KiB	390.10 KiB
5f8ee7a3ef74bc6e32496015eb0cf13a539aedb8	22.85 KiB	411.93 KiB	389.08 KiB
69d87595b411be6c93e72de62bc47457202fb72d	20.76 KiB	393.05 KiB	372.29 KiB
e89dc54f3fd0c7ad010d9a6c7cb02ac178f3fc33	22.85 KiB	412.60 KiB	389.75 KiB
f80109876fb5910e278957499d566bc708adffe1	21.58 KiB	614.71 KiB	593.13 KiB
c0b4b714a9bc728c3452ce2627ea9b6c3275bb99	20.76 KiB	430.98 KiB	410.22 KiB
bbcbaff4d524bd3af8e88f0f245b2e4256ffca3c	22.85 KiB	414.09 KiB	391.24 KiB