Add ts-rs cargo feature to derive ts-rs

[jtran]

Part of KittyCAD/modeling-app#4860.

We need to export types to a specific file like ModelingCmd.ts so that .ts file names don't collide with the ones generated in modeling-app.

The _fix_ts_rs: () is used because when ts-rs generates a TS type for an enum variant whose struct has zero fields, it gives the type null. E.g. { tag: "MyVariantName" } & null. When you use this in TS, you can never have a TS value that's both of type { tag: "MyVariantName" } and of type null.

[codecov]

Codecov Report

Attention: Patch coverage is 0.99668% with 298 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@bd2b33a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
modeling-cmds/src/def_enum.rs	0.00%	227 Missing ⚠️
modeling-cmds/src/shared.rs	0.00%	35 Missing ⚠️
modeling-cmds/src/units.rs	0.00%	6 Missing ⚠️
modeling-cmds/src/coord.rs	0.00%	4 Missing ⚠️
modeling-cmds/src/format/gltf.rs	0.00%	4 Missing ⚠️
modeling-cmds/src/format/fbx.rs	0.00%	3 Missing ⚠️
modeling-cmds/src/format/mod.rs	0.00%	3 Missing ⚠️
modeling-cmds/src/format/ply.rs	0.00%	3 Missing ⚠️
modeling-cmds/src/format/stl.rs	0.00%	3 Missing ⚠️
modeling-cmds/src/shared/point.rs	0.00%	3 Missing ⚠️
... and 5 more

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #708   +/-   ##
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  Coverage        ?   25.37%           
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  Files           ?       35           
  Lines           ?     2093           
  Branches        ?        0           
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  Hits            ?      531           
  Misses          ?     1562           
  Partials        ?        0           

Flag	Coverage Δ
unittests	25.37% <0.99%> (?)

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