Extensions and validations for the typical service note

[cavalle]

Describe your changes

Adds extensions (br-nfse-cnae, br-nfse-iss-liability) and validations used in the "typical" (80/20) service note.

Checklist before requesting a review

• I have performed a self-review of my code.
• I have added thorough tests with at least 90% code coverage.
• I've modified or created example GOBL documents the show my changes in use, if appropriate.
• When adding or modifying a tax regime or addon, I've added links to the source of the changes either structured or in the comments.
• I've run go generate . to ensure that Schemas and Regime data are up to date.
• All linter warnings have been reviewed and fixed.
• I've been obsessive with pointer nil checks to avoid panics.
• The CHANGELOG.md has been updated with an overview of my changes.
• Requested a review from @samlown.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.48%. Comparing base (20f27e6) to head (44a3b9e).
Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #429      +/-   ##
==========================================
+ Coverage   81.45%   81.48%   +0.03%     
==========================================
  Files         232      233       +1     
  Lines       11468    11491      +23     
==========================================
+ Hits         9341     9364      +23     
  Misses       1764     1764              
  Partials      363      363              

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[samlown]

All looks good. I've made a new suggestion for the "simples-nacional" to consider.