Fix typegen raising exception

[DevTGHa]

Fix typegen raising exception

Summary

Type generation from pydantic model for the frontend was raising exception below.
This is fix for the issue.

  File "C:\dev\plugin\colourcal\backend\.venv\Lib\site-packages\pydantic\json_schema.py", line 2442, in handle_invalid_for_json_schema
    raise PydanticInvalidForJsonSchema(f'Cannot generate a JsonSchema for {error_info}')
pydantic.errors.PydanticInvalidForJsonSchema: Cannot generate a JsonSchema for core_schema.IsInstanceSchema (<class 'open_vp_cal.core.structures.ProcessingResults'>)

For further information visit https://errors.pydantic.dev/2.12/u/invalid-for-json-schema
Error: Failed to export OpenAPI schema