feat: Add flag to detect unknown named types

[runeh]

Adds a rejectUnknownNamedTypes option. If true, the generator throws if it encounters a named type that's not one of the root types.

The default value is false, so this shouldn't break anything.

[codecov-commenter]

Codecov Report

Merging #106 (f13000e) into main (1dba38f) will increase coverage by 20.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             main      #106       +/-   ##
============================================
+ Coverage   80.00%   100.00%   +20.00%     
============================================
  Files           2         2               
  Lines          35       185      +150     
  Branches        7        37       +30     
============================================
+ Hits           28       185      +157     
+ Misses          7         0        -7     

Impacted Files	Coverage Δ
src/main.ts	100.00% <100.00%> (+22.58%)	⬆️
src/util.ts	100.00% <100.00%> (ø)

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[simenandre]

Looks good! 🙏