Properly reset metric flush flag on metric emission

[markushi]

📜 Description

The flush schedule flag wasn't properly reset and thus metrics weren't always sent properly.

💡 Motivation and Context

Fixes #3472
Maybe fixes #3494

💚 How did you test it?

Extended unit tests

📝 Checklist

• 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

[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	426.35 ms	498.51 ms	72.16 ms
Size	1.70 MiB	2.28 MiB	592.34 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
d6d2b2e	463.14 ms	545.56 ms	82.42 ms
a3c77bc	375.80 ms	445.85 ms	70.06 ms
c7e2fbc	377.85 ms	426.35 ms	48.50 ms
f5e1b97	362.53 ms	429.31 ms	66.78 ms
7eccfdb	389.94 ms	461.29 ms	71.35 ms
f1fdb9f	404.21 ms	496.87 ms	92.66 ms
28c9a83	346.14 ms	377.76 ms	31.62 ms
baaf637	375.71 ms	441.58 ms	65.87 ms
283d83e	348.44 ms	392.06 ms	43.62 ms
61981dc	388.65 ms	454.96 ms	66.31 ms

App size

Revision	Plain	With Sentry	Diff
d6d2b2e	1.72 MiB	2.27 MiB	555.05 KiB
a3c77bc	1.72 MiB	2.29 MiB	577.53 KiB
c7e2fbc	1.72 MiB	2.29 MiB	576.40 KiB
f5e1b97	1.70 MiB	2.28 MiB	592.00 KiB
7eccfdb	1.72 MiB	2.27 MiB	556.93 KiB
f1fdb9f	1.70 MiB	2.28 MiB	592.08 KiB
28c9a83	1.70 MiB	2.28 MiB	592.00 KiB
baaf637	1.72 MiB	2.27 MiB	558.42 KiB
283d83e	1.72 MiB	2.29 MiB	577.69 KiB
61981dc	1.70 MiB	2.28 MiB	592.12 KiB

[adinauer]

LGTM