feat: add '\0' escape sequence support in string literal parsing

Add handling for the null character escape sequence '\0' in the
readString function within the Wren compiler. This allows string
literals to include null bytes via the standard C escape syntax,
matching the existing support for other escape sequences like '\a',
'\b', and '\f'.

src/wren_compiler.c

@@ -699,6 +699,7 @@ static void readString(Parser* parser)
       {
         case '"':  addStringChar(parser, '"'); break;
         case '\\': addStringChar(parser, '\\'); break;
+        case '0':  addStringChar(parser, '\0'); break;
         case 'a':  addStringChar(parser, '\a'); break;
         case 'b':  addStringChar(parser, '\b'); break;
         case 'f':  addStringChar(parser, '\f'); break;