downgrade to sdk preview.5

[ivaylo-matov]

What does this implement/fix? Explain your changes.

• Pin SDK: Added global.json to use .NET SDK 10.0.100-preview.5.25277.114 with roll-forward disabled.
• Compiler/language: Set 12.0 in Directory.Build.props to compile with C# 12.
• Clean up toolchain: Removed
  • Microsoft.Net.Compilers.Toolset (old Roslyn override), and
  • NonCopyableAnalyzer (was raising “non-copyable” errors).

Does this close any currently open issues?

Build with the .NET 10 SDK reliably while avoiding C# 13 preview diagnostics and mismatches from an old compiler/analyzer.

Any other comments?

@zeusongit

Checklist

Check all those that are applicable and complete.

• Make sure to include one or more tests for your change
• If an enhancement PR, please create docs and at best an example
• Ensure you have signed the .NET Foundation CLA
• Add yourself to AUTHORS
• Updated the CHANGELOG

[zeusongit]

What are the changes in this file?
sorry just read the description

[ivaylo-matov]

with the .NET 10 SDK/C#13 it was raising “non-copyable” analyzer errors on our ref-struct wrappers (e.g. NewReference) and breaking the build. Dropping the analyzer unblocks the build; no product code or behavior changes - just build configuration.