Add THxI support

[tamasgal]

Adds support for integer-based histograms.

Fixes #364

[codecov]

Codecov Report

Attention: Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 84.23%. Comparing base (2a31cdf) to head (fe9f789).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/bootstrap.jl	40.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #365      +/-   ##
==========================================
- Coverage   84.71%   84.23%   -0.49%     
==========================================
  Files          21       21              
  Lines        3094     3101       +7     
==========================================
- Hits         2621     2612       -9     
- Misses        473      489      +16     

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