feat: implement floating-point number literal parsing and arithmetic operations

Add support for floating-point number literals in the parser by detecting decimal points with trailing digits in `readNumber()`, and switch the compiler's `number()` function from `strtol` to `strtod` for proper double conversion. Update the `num_abs` primitive to use `fabs()` instead of manual negation. Extend test coverage across arithmetic, comparison, equality, modulus, and string conversion tests with floating-point cases, and add a new test for decimal point at end-of-file error detection.

test/number_equality.wren

@@ -1,6 +1,7 @@
 io.write(123 == 123)  // expect: true
 io.write(123 == 124)  // expect: false
 io.write(-3 == 3)     // expect: false
+io.write(0 == -0)     // expect: true
 
 // Not equal to other types.
 io.write(123 == "123") // expect: false
@@ -10,10 +11,9 @@ io.write(0 == false)   // expect: false
 io.write(123 != 123)  // expect: false
 io.write(123 != 124)  // expect: true
 io.write(-3 != 3)     // expect: true
+io.write(0 != -0)     // expect: false
 
 // Not equal to other types.
 io.write(123 != "123") // expect: true
 io.write(1 != true)    // expect: true
 io.write(0 != false)   // expect: true
-
-// TODO(bob): Should 0 == -0?