[repo-assist] Recognize netcoreapp6.0-10.0 monikers when detecting platforms

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Closes #4239

Root cause

Some NuGet packages (e.g. AWSSDK.Core) ship assets under nonstandard nuspec target-framework monikers such as .netcoreapp8.0 instead of the recommended net8.0. Paket's platform-detection pattern match in FrameworkHandling.fs had a special case only for "netcoreapp5.0" (mapping it to .NET 5), but no equivalent case for netcoreapp6.0, 7.0, 8.0, 9.0 or 10.0. Once the leading dot is normalized away, these monikers fell through to the generic DotNetCoreApp pattern, whose backing DotNetCoreAppVersion type only covers versions 1.0–3.1, so parsing failed and Paket emitted "Could not detect any platforms from ...".

Fix

Added explicit match cases for netcoreapp6.0 through netcoreapp10.0, mapping each to the corresponding DotNetFramework FrameworkVersion.Vx, consistent with the existing netcoreapp5.0 special case.

Trade-offs

This is a minimal, surgical addition alongside the existing special-case pattern rather than a broader refactor of DotNetCoreAppVersion to support post-3.1 versions generically. That keeps the change low-risk, matching the precedent already set for netcoreapp5.0.

Test Status

• Added six new unit tests in tests/Paket.Tests/Versioning/PlatformMatchingSpecs.fs for .netcoreapp6.0 through .netcoreapp10.0.
• dotnet test tests/Paket.Tests/Paket.Tests.fsproj --filter "FullyQualifiedName~PlatformMatchingSpecs" -c Release: 58/58 passed on net10.0.
• The net461 test pass could not run in this sandbox (mono host unavailable), which is an environment limitation unrelated to this change, not a test failure.

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