Apollo v2 BeforeSpanCallback: Allow returning null

[markushi]

📜 Description

Adds nullability to BeforeSpanCallback callback

💡 Motivation and Context

Fixes #2149

💚 How did you test it?

Added 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	311.14 ms	351.46 ms	40.32 ms
Size	1.72 MiB	2.29 MiB	576.28 KiB

[codecov]

Codecov Report

Patch coverage: 87.43% and project coverage change: +0.19% 🎉

Comparison is base (9020d1b) 81.26% compared to head (a723174) 81.45%.
Report is 43 commits behind head on feat/7.0.0.

Additional details and impacted files

@@               Coverage Diff                @@
##             feat/7.0.0    #2890      +/-   ##
================================================
+ Coverage         81.26%   81.45%   +0.19%     
- Complexity         4560     4661     +101     
================================================
  Files               350      354       +4     
  Lines             16866    17155     +289     
  Branches           2272     2321      +49     
================================================
+ Hits              13706    13974     +268     
- Misses             2219     2231      +12     
- Partials            941      950       +9     

Files Changed	Coverage Δ
...racing/SentrySpanClientHttpRequestInterceptor.java	0.00% <0.00%> (ø)
...ebflux/SentryWebFilterWithThreadLocalAccessor.java	0.00% <0.00%> (ø)
...racing/SentrySpanClientHttpRequestInterceptor.java	0.00% <0.00%> (ø)
sentry/src/main/java/io/sentry/Breadcrumb.java	85.04% <ø> (ø)
sentry/src/main/java/io/sentry/HostnameCache.java	90.69% <ø> (ø)
sentry/src/main/java/io/sentry/Hub.java	75.17% <ø> (ø)
.../src/main/java/io/sentry/JsonObjectSerializer.java	84.21% <ø> (ø)
...ry/src/main/java/io/sentry/ProfilingTraceData.java	78.51% <ø> (ø)
.../main/java/io/sentry/ProfilingTransactionData.java	52.52% <ø> (ø)
sentry/src/main/java/io/sentry/Scope.java	96.72% <0.00%> (-0.36%)	⬇️
... and 83 more

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