refactor: optimize grouping

[mdjastrzebski]

Summary

Optimize grouping in order to reduce unnecessary wrapping in (?:...). Elements are categorized into 3 priorities:

• atoms: single characters, \d, ranges ([...]), groups ((?:...))
• sequences of atoms, e.g., abc
• alternations: groups of sequences/atoms joined by OR (|) operator, e.g., ab|c|d

Introduces RegexNode type to track both pattern and priority of compilation nodes during the recursive compilation steps.

Test plan

Add relevant tests, adjust existing tests.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (576f566) 100.00% compared to head (d822a96) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #23   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            8        10    +2     
  Lines           68        97   +29     
  Branches        11        19    +8     
=========================================
+ Hits            68        97   +29     

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