CASTKIT-2: Update Castkit::Types::Base.cast! to match documentation

[bnlucas]

Update type validation to support callable validators with different arities detailed in #9

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.42%. Comparing base (284bdaf) to head (eb7cb60).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #13   +/-   ##
=======================================
  Coverage   71.42%   71.42%           
=======================================
  Files           1        1           
  Lines           7        7           
=======================================
  Hits            5        5           
  Misses          2        2           

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