Add support for callable choices (#73)

[sevdog]

Short description

Adds support for callable choices (see #73).

Proposed changes

By evaluating field.choices into a list and by using this list for other checks it enables to support lazy choices like callable which were introduced in django 5.0 release.

Resolved issues

Fixes: #73

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1a1b1a8) to head (5a63f78).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #82   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          325       326    +1     
=========================================
+ Hits           325       326    +1     

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