fix: Too long flush duration

[philipphofmann]

📜 Description

Move the calculation of the flush dispatch time to the beginning of the flush function to avoid any code until the call to dispatch_group_wait adds up to the total flush duration.

💡 Motivation and Context

Fixes GH-2334, GH-2340

💚 How did you test it?

Unit tests, and GH actions dummy matrix.

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• Review from the native team if needed
• No breaking changes

🔮 Next steps

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1213.49 ms	1229.54 ms	16.05 ms
Size	20.75 KiB	368.01 KiB	347.26 KiB

Baseline results on branch: master

Startup times

Revision	Plain	With Sentry	Diff
c929040	1254.84 ms	1278.42 ms	23.58 ms
e43ce74	1235.77 ms	1252.06 ms	16.29 ms
0979ac6	1217.96 ms	1244.88 ms	26.92 ms
7d746c3	1220.78 ms	1249.47 ms	28.69 ms
202334c	1265.41 ms	1277.34 ms	11.93 ms
64225be	1213.96 ms	1227.62 ms	13.66 ms
d883642	1215.39 ms	1242.78 ms	27.39 ms
d47c2c0	1264.73 ms	1271.88 ms	7.15 ms
8607e67	1255.80 ms	1259.50 ms	3.70 ms
0fdf0b2	1194.37 ms	1227.90 ms	33.53 ms

App size

Revision	Plain	With Sentry	Diff
c929040	20.51 KiB	333.10 KiB	312.59 KiB
e43ce74	20.51 KiB	335.49 KiB	314.99 KiB
0979ac6	20.50 KiB	342.31 KiB	321.81 KiB
7d746c3	20.50 KiB	343.46 KiB	322.96 KiB
202334c	20.51 KiB	331.79 KiB	311.28 KiB
64225be	20.50 KiB	339.02 KiB	318.52 KiB
d883642	20.50 KiB	338.99 KiB	318.49 KiB
d47c2c0	20.50 KiB	342.31 KiB	321.80 KiB
8607e67	20.50 KiB	338.99 KiB	318.49 KiB
0fdf0b2	20.51 KiB	332.90 KiB	312.39 KiB

Previous results on branch: fix/flush-duration

Startup times

Revision	Plain	With Sentry	Diff
eb6e60b	1231.27 ms	1256.12 ms	24.85 ms
eb8008d	1201.45 ms	1228.34 ms	26.89 ms
d2323d1	1223.55 ms	1249.10 ms	25.55 ms
25606a4	1205.26 ms	1229.68 ms	24.42 ms
7ed4aef	1228.40 ms	1241.92 ms	13.52 ms

App size

Revision	Plain	With Sentry	Diff
eb6e60b	20.75 KiB	368.02 KiB	347.26 KiB
eb8008d	20.75 KiB	368.02 KiB	347.26 KiB
d2323d1	20.75 KiB	368.01 KiB	347.26 KiB
25606a4	20.75 KiB	368.02 KiB	347.26 KiB
7ed4aef	20.75 KiB	368.02 KiB	347.26 KiB