♻️ Update type handling in Argument classes (#27)

[edornd]

Rewritten type handling mechanism:

• type and metavar handled in different ways
• multiple subtypes supported through pydantic (e.g., dates, emails)
• less error prone, more versatile

[codecov[bot]]

Codecov Report

Merging #30 (84dbfcb) into main (94ab837) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #30   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           15        15           
  Lines          508       511    +3     
=========================================
+ Hits           508       511    +3     

Impacted Files	Coverage Δ
argdantic/parsing/__init__.py	100.00% <ø> (ø)
argdantic/parsing/arguments.py	100.00% <100.00%> (ø)
argdantic/utils.py	100.00% <100.00%> (ø)

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