Warn on complex altkey types

[MarcusRisanger]

Closes #48 .

• This fix adds a type checker for alternate key columns
• If complex types are found in the columns that comprise the alternate key, the user is warned that these should ideally be serialized prior to calling upsert.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.67%. Comparing base (1e92c53) to head (bf4a18e).

Additional details and impacted files

@@            Coverage Diff            @@
##           main      #50       +/-   ##
=========================================
+ Coverage      0   91.67%   +91.67%     
=========================================
  Files         0       17       +17     
  Lines         0      901      +901     
=========================================
+ Hits          0      826      +826     
- Misses        0       75       +75     

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