refactor: add SqlKata for SQL generation, move connection handling into ModelRepository

PluralKit.Core/Database/Utils/QueryPatchWrapper.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Collections.Generic;
+
+using SqlKata;
+
+namespace PluralKit.Core
+{
+    internal class QueryPatchWrapper
+    {
+        private Dictionary<string, object> _dict = new();
+
+        public QueryPatchWrapper With<T>(string columnName, Partial<T> partialValue)
+        {
+            if (partialValue.IsPresent)
+                _dict.Add(columnName, partialValue);
+
+            return this;
+        }
+
+        public Query ToQuery(Query q) => q.AsUpdate(_dict);
+    }
+
+    internal static class SqlKataExtensions
+    {
+        internal static Query ApplyPatch(this Query query, Func<QueryPatchWrapper, QueryPatchWrapper> func)
+            => func(new QueryPatchWrapper()).ToQuery(query);
+    }
+}