fix: Flush directly after capturing envelopes

[philipphofmann]

📜 Description

Calling flush directly after capturing any envelope did not ensure that the SDK flushes the captured envelope. This is fixed now.

💡 Motivation and Context

This came up when fixing UI tests for capturing the transaction on a background thread: #3892. I think this caused the unit tests for flush to be flaky. I enabled them again. If they are again flaky, we have to disable them again.

💚 How did you test it?

Unit tests.

📝 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 90.868%. Comparing base (8cbdf25) to head (6f6ca7c).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3915       +/-   ##
=============================================
+ Coverage   90.753%   90.868%   +0.115%     
=============================================
  Files          593       594        +1     
  Lines        46038     46061       +23     
  Branches     16418     16432       +14     
=============================================
+ Hits         41781     41855       +74     
+ Misses        4187      4136       -51     
  Partials        70        70               

Files	Coverage Δ
SentryTestUtils/ClearTestState.swift	100.000% <100.000%> (ø)
SentryTestUtils/SentryLogExtensions.swift	100.000% <100.000%> (ø)
Sources/Sentry/SentryHttpTransport.m	98.181% <100.000%> (+0.022%)	⬆️
Sources/Sentry/SentryTransportFactory.m	100.000% <100.000%> (ø)
...Tests/Integrations/ANR/SentryANRTrackerTests.swift	85.185% <100.000%> (ø)
...ns/Performance/SentryPerformanceTrackerTests.swift	100.000% <100.000%> (ø)
...tryTests/Networking/SentryHttpTransportTests.swift	99.667% <100.000%> (+3.069%)	⬆️
Tests/SentryTests/SentryHubTests.swift	98.850% <100.000%> (ø)
...Tests/TestUtils/TestConncurrentModifications.swift	100.000% <100.000%> (ø)

... and 8 files with indirect coverage changes

---

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1245.02 ms	1253.78 ms	8.76 ms
Size	21.58 KiB	616.86 KiB	595.28 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
7fb7afb	1235.00 ms	1256.81 ms	21.81 ms
a9103fe	1265.47 ms	1267.37 ms	1.90 ms
725565a	1234.59 ms	1250.02 ms	15.43 ms
2b19b82	1212.94 ms	1252.84 ms	39.90 ms
965db8a	1212.94 ms	1233.41 ms	20.47 ms
fc163f5	1198.05 ms	1227.76 ms	29.71 ms
b16d18c	1245.60 ms	1250.94 ms	5.34 ms
1734d1b	1198.69 ms	1221.62 ms	22.93 ms
addcf42	1247.33 ms	1253.58 ms	6.25 ms
f715499	1234.26 ms	1259.40 ms	25.14 ms

App size

Revision	Plain	With Sentry	Diff
7fb7afb	20.76 KiB	419.69 KiB	398.94 KiB
a9103fe	20.76 KiB	426.95 KiB	406.19 KiB
725565a	20.76 KiB	426.11 KiB	405.35 KiB
2b19b82	21.58 KiB	542.18 KiB	520.59 KiB
965db8a	22.84 KiB	403.24 KiB	380.39 KiB
fc163f5	20.76 KiB	436.30 KiB	415.54 KiB
b16d18c	20.76 KiB	437.12 KiB	416.36 KiB
1734d1b	21.58 KiB	418.82 KiB	397.24 KiB
addcf42	22.85 KiB	413.42 KiB	390.57 KiB
f715499	20.76 KiB	427.23 KiB	406.47 KiB

Previous results on branch: fix/flush-directly-after-capture

Startup times

Revision	Plain	With Sentry	Diff
840f529	1219.44 ms	1240.42 ms	20.98 ms
8621dd7	1331.67 ms	1377.76 ms	46.09 ms
7c38a5b	1237.53 ms	1261.33 ms	23.80 ms
7d94f14	1230.35 ms	1252.16 ms	21.81 ms

App size

Revision	Plain	With Sentry	Diff
840f529	21.58 KiB	616.82 KiB	595.24 KiB
8621dd7	21.58 KiB	615.95 KiB	594.37 KiB
7c38a5b	21.58 KiB	616.87 KiB	595.29 KiB
7d94f14	21.58 KiB	616.76 KiB	595.18 KiB