feat: implement scientific notation parsing for number literals in wren compiler

Add support for parsing scientific notation (e.g., 2.55e2, -2.55e-2) in the
readNumber function of wren_compiler.c. The implementation handles optional
negative exponents, validates that exponent digits follow 'e'/'E', and emits
a lex error for unterminated scientific notation. Also adds comprehensive
test cases covering valid scientific literals, missing exponents, floating
exponents, missing fractional parts, and multiple exponents.

test/language/number/literals.wren

@@ -6,5 +6,4 @@ IO.print(-0)      // expect: -0
 IO.print(123.456) // expect: 123.456
 IO.print(-0.001)  // expect: -0.001
 
-// TODO: Scientific notation?
 // TODO: Literals at and beyond numeric limits.