feat(metrics): Add BeforeEmitMetrics callback

[philipphofmann]

📜 Description

Add the BeforeEmitMetrics to the options, as described in develop docs https://develop.sentry.dev/sdk/metrics/#hooks.

💡 Motivation and Context

So users can discard metrics if they want to.

💚 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

[github-actions]

	Messages
📖	Do not forget to update Sentry-docs with your feature once the pull request gets approved.

Generated by 🚫 dangerJS against b316400

[codecov]

Codecov Report

Attention: Patch coverage is 94.38202% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 89.568%. Comparing base (96eb740) to head (b316400).

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #3799       +/-   ##
=============================================
+ Coverage   89.507%   89.568%   +0.061%     
=============================================
  Files          560       560               
  Lines        60739     60807       +68     
  Branches     21837     21866       +29     
=============================================
+ Hits         54366     54464       +98     
+ Misses        5446      5417       -29     
+ Partials       927       926        -1     

Files	Coverage Δ
Sources/Sentry/SentryHub.m	98.613% <100.000%> (+0.002%)	⬆️
Sources/Sentry/SentryOptions.m	97.717% <100.000%> (+0.014%)	⬆️
...urces/Swift/Metrics/BucketsMetricsAggregator.swift	100.000% <100.000%> (ø)
Sources/Swift/Metrics/SentryMetricsAPI.swift	100.000% <100.000%> (ø)
Tests/SentryTests/SentrySDKTests.swift	93.687% <100.000%> (+0.138%)	⬆️
...s/Swift/Metrics/BucketMetricsAggregatorTests.swift	100.000% <100.000%> (ø)
...tryTests/Swift/Metrics/SentryMetricsAPITests.swift	99.056% <80.000%> (-0.944%)	⬇️
Tests/SentryTests/SentryOptionsTest.m	97.394% <71.428%> (-0.401%)	⬇️

... and 15 files with indirect coverage changes

---

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1244.20 ms	1256.31 ms	12.10 ms
Size	21.58 KiB	573.17 KiB	551.59 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
2a894d5	1211.02 ms	1236.72 ms	25.70 ms
c471221	1244.57 ms	1257.94 ms	13.37 ms
6e1452d	1241.69 ms	1253.47 ms	11.78 ms
16450b8	1196.33 ms	1217.26 ms	20.93 ms
c0b4b71	1218.16 ms	1251.28 ms	33.12 ms
7fb7afb	1235.00 ms	1256.81 ms	21.81 ms
e681215	6240.94 ms	6254.36 ms	13.42 ms
60d6cec	1257.14 ms	1273.92 ms	16.78 ms
c00eafe	1253.04 ms	1256.41 ms	3.37 ms
c6773e5	1222.48 ms	1240.02 ms	17.54 ms

App size

Revision	Plain	With Sentry	Diff
2a894d5	21.58 KiB	414.57 KiB	392.99 KiB
c471221	22.85 KiB	413.89 KiB	391.04 KiB
6e1452d	21.58 KiB	419.68 KiB	398.10 KiB
16450b8	22.85 KiB	410.98 KiB	388.13 KiB
c0b4b71	20.76 KiB	430.98 KiB	410.22 KiB
7fb7afb	20.76 KiB	419.69 KiB	398.94 KiB
e681215	20.76 KiB	431.91 KiB	411.15 KiB
60d6cec	22.84 KiB	403.51 KiB	380.67 KiB
c00eafe	20.76 KiB	432.88 KiB	412.12 KiB
c6773e5	20.76 KiB	435.25 KiB	414.49 KiB

Previous results on branch: feat/metrics-before-emit-metrics

Startup times

Revision	Plain	With Sentry	Diff
734807e	1201.16 ms	1215.06 ms	13.90 ms
27ff265	1236.67 ms	1250.98 ms	14.31 ms

App size

Revision	Plain	With Sentry	Diff
734807e	21.58 KiB	573.19 KiB	551.61 KiB
27ff265	21.58 KiB	573.17 KiB	551.59 KiB

[brustolin]

LGTM!!

Only one suggestion.