Add database merging feature (#906)

* add initial implementation of dbmerger

merges of user tables that have overlapping data is still unimplemented. otherwise, merging of all other tables has been implemented.

* add handling for when user feed tables overlap

* fix sqlite dll path in dbmerger build

* fix accidentally inserting rows with nonunique pks

* fix merger not handling missing columns well

* fix sort not reassigning pks

* sync merger with master

* woopsies

* w-woops again

* reset database version in config to let vrcx generate missing fields

* move to net 9 and move build folder to new build folder

* remove unneeded build configurations

* support avatar time in the merge

* csproj pains

---------

Co-authored-by: Natsumi <cmcooper123@hotmail.com>

DBMerger/SqliteExtensions.cs

@@ -0,0 +1,77 @@
+using SQLite;
+using SQLitePCL;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+
+namespace DBMerger
+{
+    // This class is made of mostly hardcoded copies from the sqlite lib.
+    // Normally this would be very bad, but since the library is long since
+    // unmaintained it shouldn't matter
+    internal static class SqliteExtensions
+    {
+        // The prepare method is private, so fetch it here
+        private static readonly MethodInfo _prepareMethod = typeof(SQLiteCommand).GetMethod("Prepare", BindingFlags.NonPublic | BindingFlags.Instance);
+
+        /// <summary>
+        /// Creates a SQLiteCommand given the command text (SQL) with arguments. Place a '?'
+        /// in the command text for each of the arguments and then executes that command.
+        /// It returns each row as an array of object primitives.
+        /// </summary>
+        /// <param name="query">
+        /// The fully escaped SQL.
+        /// </param>
+        /// <param name="args">
+        /// Arguments to substitute for the occurences of '?' in the query.
+        /// </param>
+        /// <returns>
+        /// An enumerable with one object array for each row.
+        /// </returns>
+        public static List<object[]> QueryScalars(this SQLiteConnection conn, string query, params object[] args)
+        {
+            var cmd = conn.CreateCommand(query, args);
+            return cmd.ExecuteQueryScalars(conn).ToList();
+        }
+
+        public static IEnumerable<object[]> ExecuteQueryScalars(this SQLiteCommand cmd, SQLiteConnection conn)
+        {
+            if (conn.Trace)
+            {
+                conn.Tracer?.Invoke("Executing Query: " + cmd);
+            }
+            var stmt = _prepareMethod.Invoke(cmd, []) as sqlite3_stmt;
+            try
+            {
+                int columnCount = SQLite3.ColumnCount(stmt);
+                if (SQLite3.ColumnCount(stmt) < 1)
+                {
+                    throw new InvalidOperationException("QueryScalars should return at least one column");
+                }
+                while (SQLite3.Step(stmt) == SQLite3.Result.Row)
+                {
+                    var row = new object[columnCount];
+                    for (int i = 0; i < columnCount; i++)
+                    {
+                        var colType = SQLite3.ColumnType(stmt, i);
+                        row[i] = colType switch
+                        {
+                            SQLite3.ColType.Integer => SQLite3.ColumnInt(stmt, i),
+                            SQLite3.ColType.Float => (float)SQLite3.ColumnDouble(stmt, i),
+                            SQLite3.ColType.Text => SQLite3.ColumnString(stmt, i),
+                            SQLite3.ColType.Blob => SQLite3.ColumnByteArray(stmt, i),
+                            SQLite3.ColType.Null or _ => null
+                        };
+                    }
+                    yield return row;
+                }
+            }
+            finally
+            {
+                SQLite3.Finalize(stmt);
+            }
+        }
+
+    }
+}