ref: Use a callback for SentryFileManager

[noahsmartin]

This makes SentryFileManager a bit more Swifty by using a callback instead of delegate, it also will make the Swift migration more straightforward.

#skip-changelog

Closes #6172

[github-actions]

🚨 Detected changes in high risk code 🚨

High-risk code can easily blow up and is hard to test. We had severe bugs in the past. Be extra careful when changing these files, and have an extra careful look at these:

• Sources/Sentry/SentryFileManager.m

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@4f5b2c9). Learn more about missing BASE report.
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #6171   +/-   ##
========================================
  Coverage        ?   86.745%           
========================================
  Files           ?       435           
  Lines           ?     37073           
  Branches        ?     17401           
========================================
  Hits            ?     32159           
  Misses          ?      4871           
  Partials        ?        43           

Files with missing lines	Coverage Δ
Sources/Sentry/SentryFileManager.m	91.666% <100.000%> (ø)
Sources/Sentry/SentryHttpTransport.m	98.245% <100.000%> (ø)

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1244.63 ms	1270.90 ms	26.26 ms
Size	23.75 KiB	971.98 KiB	948.23 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
fd5961e	1210.59 ms	1235.57 ms	24.98 ms
f5d202b	1237.90 ms	1259.49 ms	21.59 ms
718c372	1220.09 ms	1235.15 ms	15.06 ms
52f3b6e	1219.57 ms	1239.70 ms	20.13 ms
37183fe	1212.33 ms	1238.92 ms	26.59 ms
d66f082	1227.08 ms	1247.04 ms	19.96 ms
1b9991e	1233.45 ms	1256.61 ms	23.17 ms
9be5373	1215.92 ms	1239.44 ms	23.52 ms
87fb58a	1233.12 ms	1257.17 ms	24.04 ms
5196f0d	1213.35 ms	1231.37 ms	18.02 ms

App size

Revision	Plain	With Sentry	Diff
fd5961e	23.74 KiB	874.07 KiB	850.32 KiB
f5d202b	23.75 KiB	904.53 KiB	880.78 KiB
718c372	23.75 KiB	920.65 KiB	896.90 KiB
52f3b6e	23.75 KiB	920.54 KiB	896.79 KiB
37183fe	23.75 KiB	913.63 KiB	889.87 KiB
d66f082	23.75 KiB	928.85 KiB	905.10 KiB
1b9991e	23.75 KiB	908.01 KiB	884.26 KiB
9be5373	23.75 KiB	866.50 KiB	842.75 KiB
87fb58a	23.75 KiB	919.91 KiB	896.16 KiB
5196f0d	23.75 KiB	876.93 KiB	853.19 KiB