[issue-300] Fix for Unmanaged Structs Using GenerateType.VersionTolerant (MEMPACK041)

[kostasbesson]

I’ve resolved the issue where unmanaged structs were incorrectly allowed to use GenerateType.VersionTolerant with the following updates:

1. Diagnostic MEMPACK041: Triggers an error when an unmanaged struct is marked with VersionTolerant, as unmanaged structs should remain unchanged and cannot support version-tolerant serialization.
2. Generator Fix: The generator now correctly raises an error for unmanaged structs to ensure backward compatibility.
3. Unit Test: Added MEMPACK041_UnmanagedStructCannotBeVersionTolerant to validate the behavior.

Please review and provide feedback. Looking forward to improving MemoryPack’s reliability with this fix.

[neuecc]

thanks, I'll check soon.

[Rurouni]

Hi @neuecc will you have time to merge it and publish a new version this week? Thank you!

[neuecc]

I'm currently cleaning up the issues, and I was thinking of releasing a bundle of various things,
but yeah, there's no problem with that, so let's release just the PR merged ones first.