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.

test/number/ceil.wren

@@ -1,8 +1,8 @@
-IO.print(123.ceil)    // expect: 123
-IO.print(-123.ceil)   // expect: -123
-IO.print(0.ceil)      // expect: 0
-IO.print(-0.ceil)     // expect: -0
-IO.print(0.123.ceil)  // expect: 1
-IO.print(12.3.ceil)   // expect: 13
-IO.print(-0.123.ceil) // expect: -0
-IO.print(-12.3.ceil)  // expect: -12
+IO.print(123.ceil)      // expect: 123
+IO.print((-123).ceil)   // expect: -123
+IO.print(0.ceil)        // expect: 0
+IO.print((-0).ceil)     // expect: -0
+IO.print(0.123.ceil)    // expect: 1
+IO.print(12.3.ceil)     // expect: 13
+IO.print((-0.123).ceil) // expect: -0
+IO.print((-12.3).ceil)  // expect: -12