feat: where for maps; various small fixes

[danielgtaylor]

This PR:

• Adds a where clause for maps
• Adds a .length for maps to get the number of pairs (removed due to ambiguity)
• Updates convenience functions to take any instead of map[string]any
• Provides better error messages

[codecov-commenter]

Codecov Report

Base: 73.09% // Head: 74.76% // Increases project coverage by +1.66% 🎉

Coverage data is based on head (20718b9) compared to base (194704c).
Patch coverage: 89.28% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
+ Coverage   73.09%   74.76%   +1.66%     
==========================================
  Files           7        7              
  Lines        1022     1046      +24     
==========================================
+ Hits          747      782      +35     
+ Misses        212      203       -9     
+ Partials       63       61       -2     

Impacted Files	Coverage Δ
typecheck.go	78.73% <80.00%> (+6.51%)	⬆️
expr.go	100.00% <100.00%> (ø)
interpreter.go	73.35% <100.00%> (+2.12%)	⬆️

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