Add FixedSizeBitArray

[oscardssmith]

This arguably should be 2 separate PRs, the first splits the code in this repo into files for better separation of concerns, while the 2nd (and only functional change) adds a new FixedSizeBitArray that is similar to a regular BitArray, but is fixed size, and makes sure that columns don't alias each-other (by giving each column it's own chunk). This slightly complicates indexing, but it makes lots of matrix operations a lot faster since you can broadcast views of the columns with each-other without worrying about columns clobbering each other.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.73%. Comparing base (810c0a0) to head (e00a970).
⚠️ Report is 72 commits behind head on main.

Files with missing lines	Patch %	Lines
src/FixedSizeBitArray.jl	0.00%	45 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #75       +/-   ##
===========================================
- Coverage   98.71%   82.73%   -15.98%     
===========================================
  Files           3        4        +1     
  Lines         233      278       +45     
===========================================
  Hits          230      230               
- Misses          3       48       +45     

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[nsajko]

This arguably should be 2 separate PRs

Why not split it up?

[oscardssmith]

I probably will

[giordano]

Some tests would be good now 🙂

[oschulz]

Closes #155