Migrate to clang-format 21.1.8

[jeromekelleher]

Closes #3385

[codecov]

Codecov Report

❌ Patch coverage is 95.65217% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.76%. Comparing base (dc394d7) to head (91856da).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
c/tskit/tables.c	87.50%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3389      +/-   ##
==========================================
- Coverage   89.76%   89.76%   -0.01%     
==========================================
  Files          29       29              
  Lines       31286    31285       -1     
  Branches     5738     5738              
==========================================
- Hits        28083    28082       -1     
  Misses       1794     1794              
  Partials     1409     1409              

Flag	Coverage Δ
c-tests	86.77% <95.34%> (-0.01%)	⬇️
lwt-tests	80.38% <100.00%> (ø)
python-c-tests	87.12% <100.00%> (ø)
python-tests	98.84% <ø> (ø)
python-tests-no-jit	33.46% <ø> (ø)
python-tests-numpy1	50.24% <ø> (ø)

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

Files with missing lines	Coverage Δ
c/tskit/core.c	95.63% <100.00%> (ø)
c/tskit/haplotype_matching.c	84.55% <100.00%> (ø)
c/tskit/trees.c	90.99% <100.00%> (-0.01%)	⬇️
python/_tskitmodule.c	87.12% <100.00%> (ø)
python/lwt_interface/tskit_lwt_interface.h	81.56% <100.00%> (ø)
c/tskit/tables.c	83.08% <87.50%> (ø)

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[jeromekelleher]

I think this is a step in the right direction --- pinning clang-format in the dev environment gets it in place for running local linting.