rand: fix leaks with -autofree

vlib/rand/wyrand/wyrand.v

@@ -22,6 +22,12 @@ mut:
 	extra     u32
 }
 
+// free should be called when the generator is no longer needed
+[unsafe]
+pub fn (mut rng WyRandRNG) free() {
+	unsafe { free(rng) }
+}
+
 // seed sets the seed, needs only two `u32`s in little-endian format as [lower, higher].
 pub fn (mut rng WyRandRNG) seed(seed_data []u32) {
 	if seed_data.len != 2 {