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.

test/language/number/scientific_float_missing_exponent.wren

@@ -0,0 +1 @@
+var x = 1.2e // expect error

test/language/number/scientific_floating_exponant.wren

@@ -0,0 +1 @@
+var x = 1.2e3.4 // expect error

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

test/language/number/scientific_missing_exponent.wren

@@ -0,0 +1 @@
+var x = 1e // expect error

test/language/number/scientific_missing_fractional_part.wren

@@ -0,0 +1 @@
+var x = 1.e // expect runtime error: Num does not implement 'e'.

test/language/number/scientific_multiple_exponants.wren

@@ -0,0 +1 @@
+var x = 1.2e3e4 // expect error