Add support for leap days in year_rollover_helper

[JSCU-CNI]

This PR adds support for leap days in year_rollover_helper and generally makes the function more robust when encountering invalid dates.

[codecov]

Codecov Report

Attention: Patch coverage is 28.57143% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.11%. Comparing base (c0cae58) to head (633e5e7).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/target/helpers/utils.py	28.57%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1081      +/-   ##
==========================================
- Coverage   79.12%   79.11%   -0.01%     
==========================================
  Files         341      341              
  Lines       30176    30181       +5     
==========================================
+ Hits        23877    23878       +1     
- Misses       6299     6303       +4     

Flag	Coverage Δ
unittests	79.11% <28.57%> (-0.01%)	⬇️

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[Schamper]

That must've been fun to debug 😄.