Ensure consistent sampleRand per trace

[buenaflor]

📜 Description

We want to ensure that spans within a trace are consistently sampled otherwise we might end up with traces that have missing transactions

💡 Motivation and Context

Fixes #3052

💚 How did you test it?

📝 Checklist

• I reviewed submitted code
• I added tests to verify changes
• No new PII added or SDK only sends newly added PII if sendDefaultPii is enabled
• I updated the docs if needed
• All tests passing
• No breaking changes

🔮 Next steps

[codecov]

Codecov Report

Attention: Patch coverage is 93.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 87.84%. Comparing base (e843899) to head (e63d459).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
dart/lib/src/hub_adapter.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3079      +/-   ##
==========================================
- Coverage   87.89%   87.84%   -0.06%     
==========================================
  Files         287      285       -2     
  Lines        9751     9688      -63     
==========================================
- Hits         8571     8510      -61     
+ Misses       1180     1178       -2     

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[github-actions]

Android Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	436.85 ms	512.17 ms	75.31 ms
Size	6.54 MiB	7.69 MiB	1.15 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
575ebaa	478.00 ms	585.76 ms	107.76 ms
ec78888	457.94 ms	519.96 ms	62.02 ms
81f83eb	471.40 ms	522.14 ms	50.74 ms
0fb3800	465.64 ms	536.77 ms	71.13 ms
e2d675d	457.92 ms	529.17 ms	71.25 ms
9b99523	456.91 ms	490.55 ms	33.64 ms
c8596a6	474.00 ms	492.96 ms	18.96 ms
73dca78	476.53 ms	522.21 ms	45.68 ms
793f4dc	462.68 ms	544.21 ms	81.53 ms
93b7728	475.28 ms	489.13 ms	13.86 ms

App size

Revision	Plain	With Sentry	Diff
575ebaa	6.54 MiB	7.69 MiB	1.15 MiB
ec78888	6.54 MiB	7.69 MiB	1.15 MiB
81f83eb	6.54 MiB	7.69 MiB	1.15 MiB
0fb3800	6.54 MiB	7.69 MiB	1.15 MiB
e2d675d	6.54 MiB	7.69 MiB	1.15 MiB
9b99523	6.54 MiB	7.69 MiB	1.15 MiB
c8596a6	6.54 MiB	7.53 MiB	1015.27 KiB
73dca78	6.54 MiB	7.69 MiB	1.15 MiB
793f4dc	6.54 MiB	7.69 MiB	1.15 MiB
93b7728	6.54 MiB	7.69 MiB	1.15 MiB