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/scientific_literals.wren

@@ -0,0 +1,9 @@
+var x = 2.55e2
+
+IO.print(x) // expect: 255
+IO.print(x + 1) // expect: 256
+IO.print(x == 255) // expect: true
+IO.print(2.55e-2 is Num) // expect: true
+IO.print(x is Num) // expect: true
+IO.print(-2.55e2) // expect: -255
+IO.print(-25500e-2) // expect: -255