impr: Stop canceling timer for manual transactions

[philipphofmann]

📜 Description

Avoid canceling the deadline timer on the main thread when there is no deadline timer when finishing a transaction.

💡 Motivation and Context

This same up while investigating #3977.

💚 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

All modified and coverable lines are covered by tests ✅

Project coverage is 91.417%. Comparing base (e9f219c) to head (90facfb).
Report is 2 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4380       +/-   ##
=============================================
- Coverage   91.443%   91.417%   -0.027%     
=============================================
  Files          629       629               
  Lines        50617     50625        +8     
  Branches     18340     18342        +2     
=============================================
- Hits         46286     46280        -6     
- Misses        4237      4250       +13     
- Partials        94        95        +1     

Files with missing lines	Coverage Δ
Sources/Sentry/SentryTracer.m	96.511% <100.000%> (+0.016%)	⬆️
...ts/SentryTests/Transaction/SentryTracerTests.swift	98.381% <100.000%> (+0.011%)	⬆️

... and 8 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e9f219c...90facfb. Read the comment docs.

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1225.39 ms	1235.14 ms	9.76 ms
Size	21.58 KiB	736.52 KiB	714.94 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d3630c3	1229.78 ms	1241.94 ms	12.16 ms
9fa25c2	1211.88 ms	1228.36 ms	16.48 ms
e71cf92	1201.69 ms	1226.52 ms	24.83 ms
b2f82fa	1237.78 ms	1256.02 ms	18.24 ms
84fdd22	1229.73 ms	1243.43 ms	13.69 ms
9cc7e7c	1231.84 ms	1245.24 ms	13.41 ms
6001822	1234.49 ms	1265.20 ms	30.71 ms
e19cca3	1211.69 ms	1231.04 ms	19.35 ms
804fd04	1224.46 ms	1243.77 ms	19.31 ms
60d6cec	1257.14 ms	1273.92 ms	16.78 ms

App size

Revision	Plain	With Sentry	Diff
d3630c3	22.84 KiB	403.19 KiB	380.34 KiB
9fa25c2	22.85 KiB	407.44 KiB	384.59 KiB
e71cf92	20.76 KiB	419.85 KiB	399.10 KiB
b2f82fa	20.76 KiB	419.62 KiB	398.86 KiB
84fdd22	21.58 KiB	683.50 KiB	661.92 KiB
9cc7e7c	22.84 KiB	403.14 KiB	380.29 KiB
6001822	22.85 KiB	410.98 KiB	388.13 KiB
e19cca3	21.58 KiB	669.74 KiB	648.16 KiB
804fd04	21.58 KiB	695.04 KiB	673.46 KiB
60d6cec	22.84 KiB	403.51 KiB	380.67 KiB