BREAKING CHANGE!: Use Microsoft OpenAPI document instead of own model

[pomianowski]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the new behavior?

Rewrite model.

[Copilot]

Pull Request Overview

This PR implements a major breaking change to rewrite the OpenAPI Client source generator to use Microsoft's OpenAPI document instead of the custom model. The change moves from a custom schema implementation to leveraging Microsoft.OpenApi libraries for parsing and processing OpenAPI specifications.

• Replaced custom OpenAPI schema models with Microsoft.OpenApi library
• Rewrote the source generator architecture to use a simpler, more direct approach
• Updated test infrastructure and added comprehensive test coverage for multiple OpenAPI versions

Reviewed Changes

Copilot reviewed 110 out of 116 changed files in this pull request and generated 2 comments.

File	Description
OpenApiClientGenerator.cs	Complete rewrite to use Microsoft.OpenApi instead of custom schema parsing
OpenApi.Client.csproj	Updated dependencies and build configuration for new architecture
OpenApi.Client.SourceGenerators.csproj	New project structure with Microsoft.OpenApi dependencies
Test files	Added comprehensive test infrastructure with support for OpenAPI 1.2-3.1 specifications

Comments suppressed due to low confidence (1)

src/OpenApi.Client.SourceGenerators/OpenApiClientGenerator.cs:56

• [nitpick] Method name 'ComputeClassForGeneration' is unclear. Consider renaming to 'ExtractMetadataFromSyntax' or 'ParseGeneratorMetadata' to better describe what the method does.

    private static SourceGeneratorMetadata? ComputeClassForGeneration(

[Copilot]

Remove unused variable 'test'. This appears to be leftover debug code that should be cleaned up.

Suggested change

	var test = 1;
	// (Line removed)

[Copilot]

Trailing comma in JSON object is invalid. Remove the comma after the 'roles' property on line 248.

Suggested change

	},
	}