Allow ORM Meta options to be lookups at runtime (not import time)

[mesozoic]

This allows the Meta class inside each ORM model to provide a callable that will be executed whenever the ORM requests one of its meta properties. The use case we have is to be able to provide API keys via global configuration singletons or environment variables which might not be loaded at import time but will be present at runtime.

Resolves #192

[codecov[bot]]

Codecov Report

Merging #268 (3efa2d6) into main (c08963e) will increase coverage by 0.00%. The diff coverage is 100.00%.

:exclamation: Current head 3efa2d6 differs from pull request most recent head dd46375. Consider uploading reports for the commit dd46375 to get more accurate results

@@           Coverage Diff           @@
##             main     #268   +/-   ##
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  Coverage   95.74%   95.75%           
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  Files          18       18           
  Lines         917      919    +2     
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+ Hits          878      880    +2     
  Misses         39       39           

Files Changed	Coverage Δ
pyairtable/orm/model.py	97.56% <100.00%> (+0.03%)	:arrow_up: