feat: Add basic math in templates and use it for checks read-data

[MarcWort]

Hi,

I needed a way to do monthly scans on part of my repositories, which required the modulo operation. While working on it, I thought some basic math template functions would be cleaner than the current, fairly hacky workaround described in the docs.

Let me know what you think, and if anything needs to change.

Thank you for this awesome project.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.73%. Comparing base (65f4135) to head (a5e331d).

Files with missing lines	Patch %	Lines
util/templates/functions.go	60.00%	6 Missing ⚠️

❌ Your patch check has failed because the patch coverage (60.00%) is below the target coverage (70.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #675      +/-   ##
==========================================
- Coverage   81.76%   81.73%   -0.03%     
==========================================
  Files         161      161              
  Lines       12009    12024      +15     
==========================================
+ Hits         9818     9827       +9     
- Misses       1692     1698       +6     
  Partials      499      499              

Flag	Coverage Δ
unittests	79.99% <60.00%> (-0.02%)	⬇️

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[MarcWort]

Added some more tests in 1af1a95