Reading request body: retarget net10.0 and move to the built-in OpenAPI generator

[vladimir-pecanac-main]

Retargets aspnetcore-webapi/ReadingRequestBody to net10.0 and moves the sample off Swashbuckle onto the built-in OpenAPI generator.

• Both projects: net8.0 to net10.0, Nullable enabled.
• Swashbuckle.AspNetCore 6.5.0 removed, Microsoft.AspNetCore.OpenApi 10.0.12 added. SwaggerUtils/RawTextRequestOperationFilter.cs and SwaggerUtils/SwaggerEnableRawTextAttribute.cs are replaced by OpenApiUtils/RawTextRequestOperationTransformer.cs (IOpenApiOperationTransformer) and OpenApiUtils/RawTextRequestAttribute.cs. GET /openapi/v1.json returns an OpenAPI 3.1.1 document whose six raw-text actions carry "text/plain": {"schema": {"type": "string"}}, and read-from-body keeps its PersonItemDto JSON schema. No UI package is added.
• RequestBodyMiddleware now takes ILogger, which removes the builder.Services.AddSingleton(typeof(ILogger), typeof(Logger)) line that existed only to satisfy the non-generic ILogger.
• The size guard reads Request.ContentLength before the body is read instead of measuring the string afterwards, and EnableBuffering is called with a bufferThreshold and a bufferLimit. A 2,000 byte POST to /Home/read-from-middleware returns 413, a 500 byte POST returns 200.
• Path checks use a null-safe Path.Value with Contains(..., StringComparison.OrdinalIgnoreCase); PersonItemDto becomes a record; the 413 literal becomes StatusCodes.Status413PayloadTooLarge; primary constructor on the middleware.
• Test packages: MSTest 4.4.0, Microsoft.NET.Test.Sdk 18.10.0, coverlet.collector 10.0.1, Moq 4.20.72, AutoFixture 4.18.1, Microsoft.AspNetCore.Mvc.Testing 10.0.12, plus nullable annotations and two Assert.AreEqual argument-order fixes.

dotnet build -c Release: 0 warnings, 0 errors. dotnet test -c Release: 7 passed, 0 failed, 0 skipped, on .NET SDK 10.0.302 / runtime 10.0.10.