Add NodeKey and NodeId

[erikzhang]

Preparing to add DHT functionality to the P2P protocol.

[cschuchardt88]

Why remove private keyword? It needs to be clear Identification of access modifier for the method visibility. Whether it be public, private, internal, and protected.

[erikzhang]

private is the default one.

[cschuchardt88]

Depends on the compilers and/or IDE environment and default configurations for them. Well I just going to saying it. I fought ever since I started working with neo to get to some kind of standard for our code. So it eliminates down time for developers, whether they be new or existing for this open source project. So everything is clean, neat, all the same and simple to understand/debug/test and add new features. So, I created an .editorconfig file with restrictions for safe pointing and stopping messy and error proven code or lazy coding from sneaking in the repo. But its seems everything that was configured and setup is all now removed. I don't think its smart to have half the code look like spaghetti or using different coding styles.

I came up with these coding rules for developers. So anyone can easy jump in and understand what is going in the code. Which we all agreed upon.
https://github.com/neo-project/.github/blob/d83897afb4fd5bd3c107a8dfd845e6dcf1e8d713/docs/neo-coding-rules.md

[erikzhang]

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/access-modifiers#class-and-struct-accessibility

According to Microsoft's official documentation, by default, class and struct members, including nested classes and structs, have private access. So it doesn't depend on the compilers and/or IDE environment.

But if you strongly insist, we can add private later. It's not a big problem.

[cschuchardt88]

This behavior is consistent across all compilers and .NET versions because it is part of the C# Language Specification enforced by the Roslyn compiler.

[ajara87]

lgtm