Use more features of C#

[DmitriyKulagin]

C# includes new features, consider using some of them:

• Implicit index access (from C#13)
• Collection expressions (from C#12)
• Something else...

Let's discuss it and approve a list of changes before implementation

[danFbach]

Perhaps add CancellationTokens to Service and Interface surfaces? it's pretty standard when using async methods throughout an application and improves overall application health and resource utilization