Add configure_sched_rr() for SCHED_RR scheduling policy

[nsk126]

Description

Implements the feature mentioned in #449 about using SCHED_RR as the thread policy.

Fixes #449

Is this user-facing behavior change?

Users can now call configure_sched_rr(priority) to set the SCHED_RR scheduling policy on a thread.

Did you use Generative AI?

Used Claude sonnet 4.5 to look up if Windows and Apple support SCHED_RR. Also used it for the commit message.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.28%. Comparing base (f2bc7ef) to head (c56e18e).

Files with missing lines	Patch %	Lines
realtime_tools/src/realtime_helpers.cpp	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #513      +/-   ##
==========================================
- Coverage   85.51%   85.28%   -0.23%     
==========================================
  Files          17       17              
  Lines        1408     1414       +6     
  Branches      128      128              
==========================================
+ Hits         1204     1206       +2     
- Misses        121      125       +4     
  Partials       83       83              

Flag	Coverage Δ
unittests	85.28% <0.00%> (-0.23%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
realtime_tools/src/realtime_helpers.cpp	37.14% <0.00%> (-1.48%)	⬇️

... and 1 file with indirect coverage changes

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[github-actions]

This PR is stale because it has been open for 45 days with no activity. Please tag a maintainer for help on completing this PR, or close it if you think it has become obsolete.