fix(session-replay): Use low priority queue for dispatch queue wrapper

[antonis]

📜 Description

Uses low-priority instead of background queues to reduce the chance of session replay internal multi-threading processes being dropped.

💡 Motivation and Context

While bumping the Cocoa SDK to v8.51.0 in React Native that contained the improved internal multi-threading of session replay we noticed that the Session Replay E2E tests were failing on iOS. Further investigation showed that the session replay processes were not being executed due to the QOS_CLASS_BACKGROUND priority on the CI environment that has limited resources. Bumping the priority to low (QOS_CLASS_UTILITY) worked as expected without compromising the improvements introduced in #5018
Note that locally on a dev machine the mentioned E2E tests do pass and we haven't managed to reproduce this edge case on a device or emulator.

💚 How did you test it?

Manual, CI

📝 Checklist

You have to check all boxes before merging:

• 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.
• I updated the wizard 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.894%. Comparing base (22e759d) to head (cafb32f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #5280       +/-   ##
=============================================
- Coverage   92.899%   92.894%   -0.005%     
=============================================
  Files          688       688               
  Lines        86275     86277        +2     
  Branches     31202     31207        +5     
=============================================
- Hits         80149     80147        -2     
- Misses        6026      6028        +2     
- Partials       100       102        +2     

Files with missing lines	Coverage Δ
Sources/Sentry/SentryDispatchFactory.m	100.000% <100.000%> (ø)
Sources/Sentry/SentrySessionReplayIntegration.m	86.981% <100.000%> (ø)
...onReplay/SentrySessionReplayIntegrationTests.swift	99.049% <100.000%> (ø)
...entryTests/Networking/SentryDispatchFactoryTests.m	100.000% <100.000%> (ø)
...Tests/Networking/SentryDispatchQueueWrapperTests.m	100.000% <100.000%> (ø)

... and 14 files with indirect coverage changes

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1225.60 ms	1244.60 ms	19.00 ms
Size	23.76 KiB	821.44 KiB	797.68 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
2172278	1229.58 ms	1245.00 ms	15.42 ms
8aec30e	1235.73 ms	1255.87 ms	20.14 ms
7fe37ab	1228.92 ms	1243.86 ms	14.94 ms
005bb4c	1237.38 ms	1255.54 ms	18.16 ms
1ae5768	1232.08 ms	1248.16 ms	16.08 ms
cb5c79c	1229.31 ms	1251.92 ms	22.61 ms
ee8b48f	1196.80 ms	1213.48 ms	16.68 ms
455619d	1231.40 ms	1237.70 ms	6.30 ms
45d3ca5	1248.27 ms	1255.48 ms	7.21 ms
39b1c35	1235.90 ms	1257.37 ms	21.47 ms

App size

Revision	Plain	With Sentry	Diff
2172278	21.58 KiB	542.28 KiB	520.70 KiB
8aec30e	21.58 KiB	616.75 KiB	595.17 KiB
7fe37ab	21.58 KiB	542.28 KiB	520.70 KiB
005bb4c	20.76 KiB	419.70 KiB	398.94 KiB
1ae5768	21.58 KiB	655.72 KiB	634.14 KiB
cb5c79c	22.30 KiB	730.30 KiB	708.00 KiB
ee8b48f	21.58 KiB	418.70 KiB	397.11 KiB
455619d	20.76 KiB	432.87 KiB	412.11 KiB
45d3ca5	20.76 KiB	427.54 KiB	406.78 KiB
39b1c35	22.85 KiB	408.88 KiB	386.03 KiB

[philprime]

LGTM, thank you for the investigation!

[antonis]

Note that the CocoaPods Integration Tests also fail on main.

[philprime]

@antonis I went ✅ after restart, so should be fine to merge