feat: add end position to token

[ianlewis]

Description:

Add the end position to the lexer token.

Related Issues:

Updates #89

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 66.66667% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.90%. Comparing base (4c998d8) to head (bacc1e5).

Files with missing lines	Patch %	Lines
parser.go	80.00%	3 Missing ⚠️
lexer/custom.go	0.00%	2 Missing ⚠️
lexer/lexer.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
- Coverage   73.12%   72.90%   -0.23%     
==========================================
  Files           4        4              
  Lines         413      417       +4     
==========================================
+ Hits          302      304       +2     
- Misses         97       99       +2     
  Partials       14       14              

Files with missing lines	Coverage Δ
lexer/lexer.go	0.00% <0.00%> (ø)
lexer/custom.go	62.60% <0.00%> (-0.27%)	⬇️
parser.go	90.90% <80.00%> (-0.62%)	⬇️

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