feat(gslice): Add MapIndexed

[Glonee]

Resolves #26

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.25%. Comparing base (81a0093) to head (9c75258).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #27      +/-   ##
==========================================
+ Coverage   95.99%   96.25%   +0.26%     
==========================================
  Files          34       34              
  Lines        4449     3823     -626     
==========================================
- Hits         4271     3680     -591     
+ Misses        137       99      -38     
- Partials       41       44       +3     

Flag	Coverage Δ
go-1.18.x	95.43% <100.00%> (+0.23%)	⬆️
go-1.19.x	95.51% <100.00%> (+0.92%)	⬆️
go-1.20.x	95.91% <100.00%> (+0.66%)	⬆️
go-1.21.x	96.04% <100.00%> (+0.52%)	⬆️
go-1.22.x	95.89% <100.00%> (+0.50%)	⬆️
go-1.23.x	95.97% <100.00%> (+0.57%)	⬆️
go-1.24.x	95.97% <100.00%> (+0.71%)	⬆️
unittests	96.25% <100.00%> (+0.26%)	⬆️

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