Several more database-y refactors

- DbConnectionFactory renamed to "Database", will now be the primary entry point for DB stuff
- Created IPKConnection interface mostly containing async extensions to IDbConnection, use this going forward
- Reworked the Connection/Command wrappers (that have performance/logging extensions)
- Probably more stuff that I forgot???

PluralKit.Core/Database/Wrappers/IPKConnection.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Data;
+using System.Data.Common;
+using System.Threading;
+using System.Threading.Tasks;
+
+using Npgsql;
+
+namespace PluralKit.Core
+{
+    public interface IPKConnection: IDbConnection, IAsyncDisposable
+    {
+        public Guid ConnectionId { get; }
+        
+        public Task OpenAsync(CancellationToken cancellationToken = default);
+        public Task CloseAsync();
+
+        public Task ChangeDatabaseAsync(string databaseName, CancellationToken ct = default);
+        
+        public ValueTask<DbTransaction> BeginTransactionAsync(CancellationToken ct = default) => BeginTransactionAsync(IsolationLevel.Unspecified, ct);
+        public ValueTask<DbTransaction> BeginTransactionAsync(IsolationLevel level, CancellationToken ct = default);
+        
+        public NpgsqlBinaryImporter BeginBinaryImport(string copyFromCommand);
+        public NpgsqlBinaryExporter BeginBinaryExport(string copyToCommand);
+
+        public void ReloadTypes();
+
+        [Obsolete] new void Open();
+        [Obsolete] new void Close();
+
+        [Obsolete] new IDbTransaction BeginTransaction();
+        [Obsolete] new IDbTransaction BeginTransaction(IsolationLevel il);
+    }
+}