Improved planner logic

[asdine]

This is a an evolution of the index selection logic
that will allow us to add more improvements in the future.
This also adds support for using a composite index with multiple
IN operators.

[codecov-commenter]

Codecov Report

Merging #428 (c1cc69d) into main (402b5a6) will increase coverage by 0.18%.
The diff coverage is 83.18%.

@@            Coverage Diff             @@
##             main     #428      +/-   ##
==========================================
+ Coverage   68.80%   68.99%   +0.18%     
==========================================
  Files          93       94       +1     
  Lines        9692     9706      +14     
==========================================
+ Hits         6669     6697      +28     
+ Misses       2299     2289      -10     
+ Partials      724      720       -4     

Impacted Files	Coverage Δ
internal/expr/operator.go	44.06% <ø> (+3.44%)	⬆️
internal/planner/optimizer.go	78.15% <ø> (+0.35%)	⬆️
internal/sql/parser/create.go	85.41% <42.85%> (-0.91%)	⬇️
internal/planner/index_selection.go	84.44% <84.44%> (ø)

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