Parse SQLite's IS and IS NOT operators

[LucaCappelletti94]

This PR adds support for SQLite accepts IS and IS NOT between arbitrary expressions. Only SQLite supports them, as far as I can tell.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.15%. Comparing base (14cbf75) to head (437a771).

Files with missing lines	Patch %	Lines
src/parser/mod.rs	93.10%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2470   +/-   ##
=======================================
  Coverage   81.14%   81.15%           
=======================================
  Files          42       42           
  Lines       33736    33764   +28     
  Branches    33736    33764   +28     
=======================================
+ Hits        27376    27402   +26     
  Misses       2797     2797           
- Partials     3563     3565    +2     

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