fix: check digit position when it is not valid

[stropitek]

• tests: clarify TD1 with document number check digit in optional part
• fix: ensure start and end of check digit is correct in field details

Closes: #72

[codecov]

Codecov Report

❌ Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.45%. Comparing base (8d0aa52) to head (d2935d3).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/parsers/parsePersonalNumberCheckDigit.ts	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
+ Coverage   89.35%   89.45%   +0.09%     
==========================================
  Files          48       48              
  Lines         451      455       +4     
  Branches      122      126       +4     
==========================================
+ Hits          403      407       +4     
  Misses         48       48              

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