Add API Verification tests

[damianh]

No description provided.

[Copilot]

Pull Request Overview

This PR introduces public API verification tests for the OAuth2Introspection authentication package and modernizes JSON serialization by replacing the custom SimpleJson library with the standard System.Text.Json API.

• Adds API verification testing using PublicApiGenerator to track public API changes
• Replaces SimpleJson with System.Text.Json throughout test utilities
• Removes the entire custom SimpleJson implementation (over 2100 lines)

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
PublicApiVerification.cs	New test class for verifying public API surface using PublicApiGenerator
PublicApiVerification.VerifyPublicApi.verified.txt	Baseline file containing the verified public API surface (1449 lines)
PipelineFactory.cs	Updated to use JsonSerializer.Serialize instead of SimpleJson
IntrospectionEndpointHandler.cs	Updated to use JsonSerializer.Serialize instead of SimpleJson
SimpleJson.cs	Removed entire custom JSON library implementation
AssemblyInfo.cs	Added console capture configuration for tests
*.csproj	Added PublicApiGenerator and Verify.XunitV3 package references

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[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

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[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

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