refactor(internal/sidekick/parser): migrate sidekick parsers to use ModelConfig

[jameslynnwu]

This commit updates parser.CreateModel to use ModelConfig instead of sidekickconfig.Config.

Part of #3662

[gemini-code-assist]

Code Review

This pull request refactors the sidekick parsers by introducing a new ModelConfig struct to decouple them from the broader sidekickconfig.Config, enhancing separation of concerns and explicitness of dependencies. While the refactoring is well-executed and clean, several security concerns were identified: file paths from configurations are used in file operations across multiple parsers without sufficient validation, which could lead to Path Traversal vulnerabilities if untrusted repositories or configurations are processed. As per repository guidelines (Rule: Sanitize inputs for code generation templates), it is strongly recommended to implement robust path validation and sanitization for all specification and configuration sources. Additionally, following repository Go style guidelines (Rule: All exported types and fields in Go should have doc comments), documentation should be added to the new ModelConfig to clarify its usage for future developers.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.35%. Comparing base (9d04c44) to head (e79ece0).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3941   +/-   ##
=======================================
  Coverage   83.35%   83.35%           
=======================================
  Files          69       69           
  Lines        6188     6188           
=======================================
  Hits         5158     5158           
  Misses        671      671           
  Partials      359      359           

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