Add typed modeling connection errors

[pierremtb]

Summary

• add stable modeling connection error codes for authentication, account access, concurrency limits, and backend disconnects
• include a human-readable detail and explicit retryability in each connection error
• expose a backward-compatible ModelingWebSocketResponse envelope while leaving the legacy WebSocketResponse unchanged
• keep EngineParams.kcl_version represented as a string in JSON Schema so API OpenAPI generation remains compatible
• prepare kittycad-modeling-cmds 0.2.232; 0.2.231 was already reserved when this branch was rebased

Stack

Consumed by KittyCAD/api#4472.

[codecov]

Codecov Report

❌ Patch coverage is 63.07692% with 24 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@da54cc1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
modeling-cmds/src/websocket.rs	63.07%	24 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1340   +/-   ##
=======================================
  Coverage        ?   36.66%           
=======================================
  Files           ?       37           
  Lines           ?     1923           
  Branches        ?        0           
=======================================
  Hits            ?      705           
  Misses          ?     1218           
  Partials        ?        0           

Flag	Coverage Δ
unittests	36.66% <63.07%> (?)

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