vlib: add [unsafe] tag to more functions: tos, string_from_wide, strings.Builder: write_bytes, free (#8766)

vlib/builtin/rune.v

@@ -51,6 +51,6 @@ pub fn (b []byte) bytestr() string {
 fn bytes2string(b []byte) string {
 	mut copy := b.clone()
 	copy << `\0`
-	res := tos(copy.data, copy.len-1)
+	res := unsafe { tos(copy.data, copy.len-1) }
 	return res
 }