First bits of the Context overhaul.

Reintroduces separate contexts for users, channels, connections (now split into sessions and connections) and user-channel associations.
It builds which is as much assurance as I can give about the stability of this commit, but its also the bare minimum of what i like to commit sooooo
A lot of things still need to be broadcast through events throughout the application in order to keep states consistent but we'll cross that bridge when we get to it.
I really need to stop using that phrase thingy, I'm overusing it.

SharpChat.SQLite/SQLiteStorage.cs

@@ -1,13 +1,14 @@
 using Microsoft.Extensions.Logging;
 using SharpChat.Configuration;
 using SharpChat.Messages;
+using SharpChat.Storage;
 using System.Data.SQLite;
 using ZLogger;
 using NativeSQLiteConnection = System.Data.SQLite.SQLiteConnection;
 
 namespace SharpChat.SQLite;
 
-public class SQLiteStorage(ILogger logger, string connString) : Storage, IDisposable {
+public class SQLiteStorage(ILogger logger, string connString) : StorageBackend, IDisposable {
     public const string MEMORY = "file::memory:?cache=shared";
     public const string DEFAULT = "sharpchat.db";