feat: support the new W3C random-trace-id flag

[herin049]

Implements #3270

Changes

Introduces an additional RANDOM flag to the TraceFlags bitfield with relevant supporting functions. Adds the is_random function to the IdGenerator trait to allow id generator implementations to specify if trace IDs are randomly generated with respect to the W3C trace context spec. These changes also add logic to add the random-trace-id flag to the current context only if there is no parent context available.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.7%. Comparing base (00e8ea7) to head (0d5dfcd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #3304   +/-   ##
=====================================
  Coverage   80.6%   80.7%           
=====================================
  Files        129     129           
  Lines      23261   23353   +92     
=====================================
+ Hits       18756   18852   +96     
+ Misses      4505    4501    -4     

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