Add .NET 10 to the CI test matrix

## Summary

ML.NET CI currently uses the .NET 11 preview SDK but runs its main test jobs on `net8.0`. Add `net10.0` test coverage because .NET 10 is the current LTS release.

## Proposed scope

- Add `net10.0` to the supported test target frameworks.
- Install the .NET 10 runtime through the repository tool set.
- Make `net10.0` the default target for the main CI test jobs.
- Keep explicit `net8.0` coverage until .NET 8 reaches end of support on November 10, 2026.
- Keep the existing .NET Framework 4.8 coverage.
- Do not change product target frameworks as part of this issue.

## Acceptance criteria

- CI builds and runs tests on `net10.0` on supported platforms and architectures.
- A representative test project passes on `net10.0`.
- Existing `net8.0` and `net48` compatibility coverage remains available.

Inspect the repository's CI workflows and tool-set configuration to find the supported test target frameworks and runtime installation steps. Update the main CI test jobs for net10.0 while preserving explicit net8.0 and net48 coverage, without changing product target frameworks. Verify a representative test project builds and passes on net10.0 across the supported platforms and architectures.

Written by the indexing model from the issue text.