Migrate to C# 10

[timheuer]

Take an opportunity to migrate to new C# language capabilities like:

• [x] #241
• [x] #242
• [x] #243

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stevenpears-bjss]

re-opening as covered by #244 - just waiting for approval