Engine: Split FHIR facade services from MVC

[losolio]

Introduce AddFhirFacadeServices for registering the FHIR facade service layer without calling AddControllers or registering MVC formatter services.

Add AddFhirFacadeMvc as the explicit replacement for the previous MVC-based facade setup, and mark AddFhirFacade obsolete so beta users get a clear migration path.

Move FHIR MVC formatter service registrations behind AddFhirMvcFormatterServices and add a contract test covering the MVC-free facade registration.

[Copilot]

Pull request overview

This PR decouples the Spark Engine “FHIR facade” service-layer registrations from ASP.NET Core MVC, enabling consumers to register the facade without implicitly adding controllers/formatters, while preserving the prior behavior behind an explicit MVC-oriented extension method.

Changes:

• Added AddFhirFacadeServices to register the FHIR facade service layer without calling AddControllers / MVC service registration.
• Added AddFhirFacadeMvc as the explicit MVC-based facade setup and marked AddFhirFacade obsolete to guide migration.
• Moved MVC formatter service registrations behind a dedicated helper and added a contract test ensuring MVC-free facade registration.

Reviewed changes

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

File	Description
Tests/Spark.Engine.R4.Tests/Extensions/FhirFacadeServiceCollectionExtensionsTests.cs	Adds a contract test verifying AddFhirFacadeServices does not register MVC/controller-related services while still registering required facade components.
Libraries/Spark.Engine/Extensions/IServiceCollectionExtensions.cs	Introduces the new facade registration APIs, routes legacy AddFhirFacade to the MVC path, and isolates MVC formatter registrations behind a helper.

Comments suppressed due to low confidence (1)

Libraries/Spark.Engine/Extensions/IServiceCollectionExtensions.cs:104

• AddFhirFacadeServicesInternal builds a temporary ServiceProvider to read configured SparkOptions, but it is never disposed. Wrap the BuildServiceProvider() result in a using/using var to avoid leaking the root provider (and any transient/singleton disposables created during resolution).

        services.Configure(options);

        var serviceProvider = services.BuildServiceProvider();
        var opts = serviceProvider.GetRequiredService<IOptions<SparkOptions>>()?.Value;
        var settings = opts.Settings;

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[losolio]

Good catch — Iremoved AddFhirMvcFormatterServices entirely in a follow-up instead. Nothing in Applications/ or Libraries/ resolves these four formatters from DI; they're constructed manually inside AddFhirFormatters (with ArrayPool.Shared) and inserted into MvcOptions.InputFormatters/OutputFormatters. The TryAddTransient lines seems to be dead code — the bug only surfaced because the new test was the first thing that tried to resolve them?