fix(stp): ship net10.0 abstractions and document target frameworks

[Copilot]

Maintenance review of target framework support for Egil.StronglyTypedPrimitives: each net9.0/net8.0/netstandard2.0 target needs an explicit decision, and CI should install only the SDKs the retained targets require.

While reviewing, I found a packaging defect: the Abstractions library multi-targets net10.0 (with a dedicated net10.0 OpenAPI schema transformer), but the package never shipped lib/net10.0. net10.0 consumers therefore fell back to the lib/net9.0 assembly, which is compiled against the incompatible Microsoft.OpenApi v1 API.

Changes

• Ship lib/net10.0 — added the missing pack item in the generator csproj. A glob that matches nothing is silently dropped, so the absent net10.0 build went unnoticed.
• Build net10.0 in CI — the create-nuget job now builds the net10.0 Abstractions before packing so the new lib/net10.0 folder is populated.
• Documented every target framework decision — added csproj comments explaining why each target is retained: netstandard2.0 is required for the Roslyn source generator; the Abstractions target net10.0/net9.0/net8.0/netstandard2.0 for consumer compatibility and per-runtime OpenAPI support.
• Multi-targeted OpenAPI v2 test pass — the integration test project now multi-targets net9.0;net10.0 so the schema transformer is exercised against both the Microsoft.OpenApi v1 API (net9.0) and the v2 API (net10.0). The transformer test is split per target framework (StronglyTypedSchemaTransformerV1Test.cs / StronglyTypedSchemaTransformerV2Test.cs) to mirror the production .net9.cs/.net10.cs convention; the v2 file asserts the JsonSchemaType enum and accounts for the now-nullable Items/Properties members. Test files keep the *Test.cs naming so the repo's test-specific analyzer rules (for example CA1707) continue to apply.

CI continues to install only the 9.x and 10.x SDK bands required by the retained targets. Validated with build, pack, package validation, and the full test suite (127 unit + 43 integration on net9.0 + 43 integration on net10.0).

[egil]

@copilot lets add a multi-targeted test pass against the Microsoft.OpenApi v2 API is a reasonable follow-up.

[Copilot]

@copilot lets add a multi-targeted test pass against the Microsoft.OpenApi v2 API is a reasonable follow-up.

Done in 26ed985. The integration test project now multi-targets net9.0;net10.0, so the schema transformer runs against the Microsoft.OpenApi v1 API (net9.0) and the v2 API (net10.0). The transformer test is split per TFM (StronglyTypedSchemaTransformerV1Test.cs / V2Test.cs) to mirror the production .net9.cs/.net10.cs split; the v2 file asserts JsonSchemaType and handles the now-nullable Items/Properties. Both passes are green (43 tests each).

[egil]

Suggested change

	using Examples;
	using Microsoft.AspNetCore.OpenApi;
	using Microsoft.Extensions.DependencyInjection;
	#if NET9_0
	using Microsoft.OpenApi.Models;
	#elseif NET10_0
	using Microsoft.OpenApi;
	#endif
	using System.Text.Json;
	using System.Text.Json.Serialization.Metadata;

@copilot There's no need to have two different test classes. I think we can just import different using statements per.NET target and keep a single test class since it looks like all the tests are the same in both this test class and the v2 test class.

[egil]

Done in 31d75d2. Merged into a single StronglyTypedSchemaTransformerTest with conditional usings. The bodies weren't fully identical (v1 uses string schema types, v2 uses the JsonSchemaType enum, and Properties/Items are nullable in v2), so the class defines per-TFM type constants and a shared AssertNoProperties helper to keep all test bodies identical. Both TFMs pass (43/43).