Insert: IList<> implementation

[viceroypenguin]

This PR adds an IList<> implementation of Insert, which improves memory usage and performance.

Fixes #455

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07 🎉

Comparison is base (5aabe4f) 91.33% compared to head (7b37066) 91.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #461      +/-   ##
==========================================
+ Coverage   91.33%   91.40%   +0.07%     
==========================================
  Files         245      245              
  Lines        7858     7916      +58     
  Branches     1603     1609       +6     
==========================================
+ Hits         7177     7236      +59     
  Misses        462      462              
+ Partials      219      218       -1     

Impacted Files	Coverage Δ
Source/SuperLinq/Insert.cs	100.00% <100.00%> (+2.70%)	⬆️

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