feat: keep Mapping type

[PrettyWood]

Change Summary

Related issue number

Checklist

• Unit tests for the changes exist
• Tests pass on CI and coverage remains at 100%
• Documentation reflects the changes where applicable
• changes/<pull request or issue id>-<github username>.md file added describing change
  (see changes/README.md for details)

[codecov-io]

Codecov Report

Merging #70 (ac2e63f) into master (5025707) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master       #70   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         4357      4383   +26     
  Branches       875       881    +6     
=========================================
+ Hits          4357      4383   +26     

Impacted Files	Coverage Δ
pydantic/fields.py	100.00% <100.00%> (ø)
pydantic/schema.py	100.00% <100.00%> (ø)

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