Do not validate nullable annotations when targeting .NET Framework

[tmat]

Issue Description

The code base currently uses ! suppression to avoid nullable warnings.
Rather than littering the code with ! the nullability analysis should be disabled for .NET Framework targets in projects that multi-target.

Alternatively, calls to APIs like string.IsNullOrEmpty that are annotated on net10 but not on .NET Framework should be changed to null-annotated equivalents.

The editorconfig suppresses IDE0370: Suppression is unnecessary to allow unnecessary ! when not targeting .NET Framework.
This should be removed.