refactor(datetime): remove Tokenizer class

[timreichen]

Changes
This PR removes the ability to add custom rules to DateTimeFormatter . This allows for simplifications:

• removes custom rules for private DateTimeFormatter class
• removes Tokenizer class in favour of formatToParts() function
• removes custom rules tests

Reasoning
The DateTimeFormatter file is private.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.21%. Comparing base (f7e3cd5) to head (1f8c78f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5622      +/-   ##
==========================================
- Coverage   96.44%   96.21%   -0.24%     
==========================================
  Files         468      468              
  Lines       38221    38152      -69     
  Branches     5542     5536       -6     
==========================================
- Hits        36864    36707     -157     
- Misses       1315     1403      +88     
  Partials       42       42              

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[iuioiua]

Nice cleanup. LGTM.

[kt3k]

LGTM

let me check a bit more