feat: rename Map::insert to Map::append and add proper insert impl

[paolobarbolini]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.40%. Comparing base (cc4f137) to head (52102ed).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
src/map.rs	66.66%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #126      +/-   ##
==========================================
- Coverage   74.85%   74.40%   -0.46%     
==========================================
  Files          30       30              
  Lines         704      715      +11     
==========================================
+ Hits          527      532       +5     
- Misses        177      183       +6     

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