bio.c: Split thread function into smaller parts v2

[TedLyngmo]

This provides an alternative to #2576

No functional changes.

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

[codecov]

Codecov Report

❌ Patch coverage is 77.14286% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.21%. Comparing base (811a644) to head (dcf6a9e).

Files with missing lines	Patch %	Lines
src/bio.c	77.14%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           unstable    #2577   +/-   ##
=========================================
  Coverage     72.21%   72.21%           
=========================================
  Files           126      126           
  Lines         70662    70671    +9     
=========================================
+ Hits          51028    51035    +7     
- Misses        19634    19636    +2     

Files with missing lines	Coverage Δ
src/bio.c	86.36% <77.14%> (+0.84%)	⬆️

... and 12 files with indirect coverage changes

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[TedLyngmo]

Hmm, I don't understand the failures:

...
[ok] - test_hashtable.c:test_iterator
[test_safe_iterator - unit/test_hashtable.c:616] Failed assertion: hashtableAdd(ht, entry + count)
[fail] - test_hashtable.c:test_safe_iterator
...
[ok] - test_hashtable.c:test_random_entry_sparse_table
[test_hashtable.c] Memory leak detected of 27792 bytes
[END] - test_hashtable.c: 17 tests, 15 passed, 2 failed

Are each PR's tests running completely isolated or could my other PR be interfering?

[TedLyngmo]

Are each PR's tests running completely isolated or could my other PR be interfering?

I now think they are not completely isolated. Running the same tests twice without having another PR going through the testing succeded.