Add packed integer vector support

[Malkovsky]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 96.89922% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.05%. Comparing base (2a43cde) to head (93d8d1f).

Files with missing lines	Patch %	Lines
include/pixie/integer_vector/packed.h	92.66%	4 Missing and 7 partials ⚠️
include/pixie/integer_vector/monotone.h	95.00%	0 Missing and 3 partials ⚠️
src/tests/integer_vector_tests.cpp	99.28%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
+ Coverage   90.66%   91.05%   +0.39%     
==========================================
  Files          47       51       +4     
  Lines       12220    12934     +714     
  Branches     1771     1828      +57     
==========================================
+ Hits        11079    11777     +698     
- Misses        533      539       +6     
- Partials      608      618      +10     

Flag	Coverage Δ
gcov	91.05% <96.89%> (+0.39%)	⬆️

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