feat: add Sequence.each method to iterate over elements with a function

Add a new `each` method to the Sequence class in the Wren programming language,
allowing iteration over sequence elements by passing each element to a provided
function. This replaces the previous pattern of using `map` with `Fiber.yield`
in examples, providing a more direct and idiomatic way to perform side effects
per element. The implementation includes a core library method in `core.wren`,
a C source string in `wren_core.c`, documentation in the Sequence markdown file,
and three test cases covering normal iteration, empty sequences, and non-function
argument error handling.

src/vm/wren_core.c

@@ -86,6 +86,12 @@ static const char* libSource =
 "    return result\n"
 "  }\n"
 "\n"
+"  each(f) {\n"
+"    for (element in this) {\n"
+"      f.call(element)\n"
+"    }\n"
+"  }\n"
+"\n"
 "  map(f) {\n"
 "    var result = new List\n"
 "    for (element in this) {\n"