✨ Support ASP.NET Core OpenAPI

[desjoerd]

Add support for ASP.NET Core OpenAPI (.NET 10).

There is one known issue around circular references which requires dotnet/aspnetcore#64109 to be merged.

[Copilot]

Pull request overview

This PR adds support for ASP.NET Core OpenAPI in .NET 10, introducing a new OptionalValues.OpenApi library that enables OptionalValue<T> types to be properly represented in OpenAPI documentation. The implementation includes a schema transformer that unwraps OptionalValue types to their underlying types while preserving nullability and validation attributes.

Key Changes

• Introduces new OptionalValues.OpenApi library targeting .NET 10 with schema transformation support
• Upgrades SDK to .NET 10 (10.0.100) and adds .NET 10 to target frameworks
• Adds comprehensive test infrastructure including a test application and integration tests

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
version.json	Bumps version to 0.8-preview and adds release configuration for preview releases
global.json	Updates SDK version to 10.0.100 for .NET 10 support
Directory.Build.props	Adds target framework variables for .NET 10 and differentiates Swashbuckle vs OpenApi frameworks
Directory.Packages.props	Adds .NET 10 package references (Microsoft.AspNetCore.OpenApi, Microsoft.AspNetCore.Mvc.Testing, Microsoft.Extensions.ApiDescription.Server)
src/OptionalValues.OpenApi/OptionalValuesSchemaTransformer.cs	Core transformer that unwraps OptionalValue types and applies schema transformations
src/OptionalValues.OpenApi/OpenApiOptionsExtensions.cs	Public API extension methods to enable OptionalValue support in OpenAPI configuration
src/OptionalValues.OpenApi/OptionalValues.OpenApi.csproj	Project file for new OpenAPI library targeting .NET 10
src/OptionalValues.OpenApi/PublicAPI.*.txt	Public API surface documentation for the new library
src/OptionalValues.Swashbuckle/OptionalValues.Swashbuckle.csproj	Updates to use Swashbuckle-specific target frameworks
test/OptionalValues.OpenApi.Tests/*	Integration test suite that validates schema generation for primitives and references
test/OptionalValues.OpenApi.TestApp/*	Test web application with sample endpoints demonstrating OptionalValue usage
test/OptionalValues.Swashbuckle.Tests/OptionalValues.Swashbuckle.Tests.csproj	Updates to use Swashbuckle-specific target frameworks
examples/OptionalValues.Examples.OpenApi/*	Example application demonstrating OptionalValue with ASP.NET Core OpenAPI
examples/OptionalValues.Examples.Swashbuckle/*	Updates Swashbuckle example with version override and regenerated OpenAPI spec
OptionalValues.slnx	Adds new OpenAPI projects to solution

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