finish implementing path parameters

SimpleHttpServer/Types/MultiKeyDictionary.cs

@@ -0,0 +1,22 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace SimpleHttpServer.Types;
+internal class MultiKeyDictionary<K1, K2, V> where K1 : notnull where K2 : notnull {
+    internal readonly Dictionary<K1, Dictionary<K2, V>> backingDict = new();
+    public MultiKeyDictionary() { }
+
+    public void Add(K1 k1, K2 k2, V value) {
+        if (!backingDict.TryGetValue(k1, out var d2))
+            d2 = new();
+        d2.Add(k2, value);
+        backingDict[k1] = d2;
+    }
+
+    public bool TryGetValue(K1 k1, K2 k2, [MaybeNullWhen(false)] out V value) {
+        if (backingDict.TryGetValue(k1, out var d2) && d2.TryGetValue(k2, out value))
+            return true;
+
+        value = default;
+        return false;
+    }
+}