bio.c: Split thread function into smaller parts

[TedLyngmo]

This provides an alternative to #2577

No functional changes.

This makes for easier reading, extending the functionality and maintenance only.

[codecov]

Codecov Report

❌ Patch coverage is 78.57143% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.16%. Comparing base (971cdb7) to head (be63369).
⚠️ Report is 1 commits behind head on unstable.

Files with missing lines	Patch %	Lines
src/bio.c	78.57%	9 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2576      +/-   ##
============================================
- Coverage     72.21%   72.16%   -0.06%     
============================================
  Files           126      126              
  Lines         70662    70680      +18     
============================================
- Hits          51031    51005      -26     
- Misses        19631    19675      +44     

Files with missing lines	Coverage Δ
src/bio.c	86.50% <78.57%> (+0.98%)	⬆️

... and 15 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.