feat: support semantic versioning for grain interfaces

[bknote71]

Summary

Add semantic versioning (SemVer) support for grain interfaces alongside the existing ushort versioning.

Motivation

The current ushort-only versioning limits grain interfaces to a simple numeric counter. This change allows developers to use SemVer strings (e.g. "1.2.0", "2.0.0-beta.1") while maintaining full backward compatibility with existing numeric versions.

Changes

• SemanticVersion struct (SemVer 2.0.0 compliant)
• GrainInterfaceVersion unified wrapper supporting both ushort and SemanticVersion
• VersionAttribute now accepts string for SemVer
• GrainVersionManifest updated to use GrainInterfaceVersion
• Message serialization updated with kind marker for protocol-level support

Backward Compatibility

• Existing [Version(2)] usage works unchanged
• GrainInterfaceVersion.Parse() auto-detects numeric vs SemVer
• Cross-kind comparison (numeric vs semantic) throws to prevent misconfiguration

Microsoft Reviewers: Open in CodeFlow

[bknote71]

@dotnet-policy-service agree

[ReubenBond]

What is the use case for this - why wouldn't numeric versions suffice?

[bknote71]

What is the use case for this - why wouldn't numeric versions suffice?

A couple of thoughts on this:

Traceability:
A bare ushort like 1026 tells you nothing about what changed
you have to look up a per-grain mapping to understand the change.
Semantic versions are self-describing: v1.2.1 immediately signals a patch on the 1.2 line.
This also makes it straightforward to aggregate changelogs by major/minor across grains.

Versioning in CI/CD:
With semantic versioning, a git tag like v1.2.1 can be injected directly into the build as the version value (no conversion or state needed.)
With ushort, you need to track the last-used number somewhere and increment it, which introduces an external dependency for version assignment itself.

[ReubenBond]

@bknote71 Could you use a comment or a custom attribute for those things? Grain interface versioning is primarily for compatibility breaks it's not intended to be informational.