fix: stop lexing negative numbers as single tokens to fix parsing of subtraction

Previously, the lexer greedily consumed a `-` followed by a digit as a single negative number token, causing "1 -1" to be lexed as two number tokens instead of a minus operator and a positive literal. This broke parsing of subtraction expressions without spaces.

Now `-` always emits a TOKEN_MINUS, and the parser handles unary negation. This is a breaking change: `-16.sqrt` is now parsed as `-(16.sqrt)` instead of `(-16).sqrt`, requiring parentheses for negative method receivers. All number method tests (abs, ceil, floor, sqrt, toString) are updated to use explicit parentheses for negative receivers.

src/wren_compiler.c

@@ -752,14 +752,7 @@ static void nextToken(Parser* parser)
         return;
 
       case '-':
-        if (isDigit(peekChar(parser)))
-        {
-          readNumber(parser);
-        }
-        else
-        {
-          makeToken(parser, TOKEN_MINUS);
-        }
+        makeToken(parser, TOKEN_MINUS);
         return;
 
       case '|':