hashmap: increase hashing speed with integer or string keys

TypeInfo.getHash is a virtual function call that is opaque to current
D compilers. Directly using object.hashOf is faster.

utils/vibe/utils/hashmap.d

@@ -28,6 +28,10 @@ struct DefaultHashMapTraits(Key) {
 			return () @trusted { return (cast(Key)k).toHash(); } ();
 		else static if (__traits(compiles, Key.init.toHashShared()))
 			return k.toHashShared();
+        else static if ((__traits(isScalar, Key) ||
+                (isArray!Key && is(Key : E[], E) && __traits(isScalar, E))) &&
+                is(typeof(() @nogc nothrow pure => .object.hashOf(k))))
+            return () @trusted { return .object.hashOf(k); }();
 		else {
 			// evil casts to be able to get the most basic operations of
 			// HashMap nothrow and @nogc