Add UseFullTypeNameSchemaIds extension for OpenAPI schema reference IDs

[Copilot]

Adds an extension method to configure OpenAPI schema reference IDs using full type names (namespace + class name) instead of just the class name, resolving naming collisions when multiple types share the same name across different namespaces.

Changes

• OpenApiExtensions.cs: Added UseFullTypeNameSchemaIds() extension method that configures CreateSchemaReferenceId to use Type.FullName, with + replaced by . for nested types
• README.md: Added usage documentation with collision scenario example
• Sample application: Added commented usage example

Usage

builder.Services.AddOpenApi(options =>
{
    options.UseFullTypeNameSchemaIds();
});

Without this extension, both MyApp.Models.User and MyApp.DTOs.User would generate a schema named "User", potentially causing conflicts. With the extension, they generate "MyApp.Models.User" and "MyApp.DTOs.User" respectively.

Notes

• Opt-in extension method, maintains backward compatibility
• Available for .NET 9.0+ only (within existing #if NET9_0_OR_GREATER block)
• No test infrastructure exists for AspNetCore extensions

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add extension method to OpenApiOptions to use full type name in schema reference ID</issue_title>
<issue_description>### Summary

Add an extension method to OpenApiOptions in the TinyHelpers.AspNetCore package to allow using the full type name in schema reference IDs, improving schema uniqueness and resolving issues when multiple types have the same name.

Motivation

As suggested in dotnet/aspnetcore#64325 (comment), using full type names in OpenAPI schema references helps to avoid naming collisions and is especially useful for complex APIs with overlapping type names.

Proposed Solution

• Implement an extension method for OpenApiOptions that configures the schema ID generation using the full type name (namespace + class).
• Add usage documentation and an example.

References

• Related suggestion: dotnet/aspnetcore#64325 (comment)

Acceptance Criteria

• Extension method implemented and unit tested
• Example usage in the documentation
• Backward compatibility verified
  </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add extension method to OpenApiOptions to use full type name in schema reference ID #290

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