feat(tracing): Propagate sample_rand to transaction's baggage

[szokeasaurusrex]

continue_trace now propagates incoming sample_rand values to the transaction's baggage. Also, in the case where sample_rand is missing from the incoming trace and needs to be backfilled, this change introduces a mechanism for the backfilled value from the scope's propagation context to be propagated to the transaction's baggage.

The transaction still does not use the sample_rand for making sampling decisions; this PR only enables propagation. A future PR will add support for reading the incoming/backfilled sample_rand and for using this value to make sampling decisions.

Depends on:

• feat(tracing): Backfill missing sample_rand on PropagationContext #4038

Ref #3998

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.63%. Comparing base (789b065) to head (ccb969e).
Report is 4 commits behind head on szokeasaurusrex/sample_rand-2.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@                        Coverage Diff                        @@
##           szokeasaurusrex/sample_rand-2    #4040      +/-   ##
=================================================================
+ Coverage                          79.56%   79.63%   +0.06%     
=================================================================
  Files                                140      140              
  Lines                              15561    15579      +18     
  Branches                            2639     2643       +4     
=================================================================
+ Hits                               12381    12406      +25     
+ Misses                              2343     2336       -7     
  Partials                             837      837              

Files with missing lines	Coverage Δ
sentry_sdk/scope.py	85.57% <100.00%> (+0.03%)	⬆️
sentry_sdk/tracing.py	77.73% <100.00%> (+0.13%)	⬆️
sentry_sdk/tracing_utils.py	85.50% <100.00%> (+0.46%)	⬆️

... and 4 files with indirect coverage changes

[sentrivana]

@szokeasaurusrex Were there relevant changes to this after Neel's last review? With the force pushes I can't tell.

[szokeasaurusrex]

@szokeasaurusrex Were there relevant changes to this after Neel's last review? With the force pushes I can't tell.

Nope, just rebasing on #4038 and updating the tests in response to the changes in that PR

[sentrivana]

lgtm