feat(mutable): adding Map, MapI, Filter, FilterI

[samber]

Adding some basic methods to mutable sub-package.

This PR introduces a new standard i would like to bring to this repo:

• Map -> without index int
• MapI -> with index int

I don't plan to make a breaking change to the main lo package in the short term.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.15%. Comparing base (677bfd1) to head (415a6a9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #577      +/-   ##
==========================================
+ Coverage   94.10%   94.15%   +0.04%     
==========================================
  Files          18       18              
  Lines        3039     3063      +24     
==========================================
+ Hits         2860     2884      +24     
  Misses        168      168              
  Partials       11       11              

Flag	Coverage Δ
unittests	94.15% <100.00%> (+0.04%)	⬆️

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