refactor(dart): migrate to ModelConfig

[jameslynnwu]

Transitions Dart generation from sidekickconfig.Config to parser.ModelConfig

Part of #3662

[gemini-code-assist]

Code Review

This pull request refactors the Dart generation logic to use parser.ModelConfig instead of sidekickconfig.Config. The changes are clean, consistent, and improve decoupling by reducing dependencies on the larger configuration structure. I've suggested one minor improvement to respect the SpecificationFormat from the library configuration instead of hardcoding it.

[gemini-code-assist]

The SpecificationFormat is currently hardcoded to "protobuf". It would be better to respect the SpecificationFormat field from the library config, which allows for other formats like "discovery". The default can remain "protobuf" if the field is not set.

Suggested change

	modelConfig := parser.ModelConfig{
	SpecificationFormat: "protobuf",
	ServiceConfig: api.ServiceConfig,
	SpecificationSource: ch.Path,
	Source: src,
	Codec: buildCodec(library),
	}
	specFormat := library.SpecificationFormat
	if specFormat == "" {
	specFormat = "protobuf"
	}
	modelConfig := parser.ModelConfig{
	SpecificationFormat: specFormat,
	ServiceConfig: api.ServiceConfig,
	SpecificationSource: ch.Path,
	Source: src,
	Codec: buildCodec(library),
	}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.35%. Comparing base (4e2fdfc) to head (c5beb3b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3947   +/-   ##
=======================================
  Coverage   83.35%   83.35%           
=======================================
  Files          69       69           
  Lines        6188     6188           
=======================================
  Hits         5158     5158           
  Misses        671      671           
  Partials      359      359           

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