refactor: migrate avoid_using_api

[solid-illiaaihistov]

Closes #249

[gemini-code-assist]

Code Review

This pull request refactors the avoid_using_api lint rule to utilize the analyzer-based RuleContext and RuleVisitorRegistry instead of custom_lint APIs. It replaces AvoidUsingApiLinter with AvoidUsingApiVisitor (extending SimpleAstVisitor), introduces several AST node helper extensions in node_utils.dart, refactors path matching in path_utils.dart, and replaces old integration tests with a comprehensive unit test suite. The review feedback suggests making the rootPath parameter in _getActiveEntries nullable to align with shouldSkipFile and passing context.package?.root.path directly instead of coalescing it to an empty string.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.