feat: implement List.addAll() method to append elements from iterable

Add `addAll(other)` method to the List class in both the Wren core library source and its embedded C string representation. The method iterates over the given `other` sequence, appends each element to the list using the existing `add()` method, and returns the original `other` argument to match the documented return behavior. Include a new test file `test/list/add_all.wren` covering basic appending, empty iterable, range input, and return value verification.

src/wren_core.c

@@ -60,6 +60,13 @@ static const char* libSource =
 "}\n"
 "\n"
 "class List is Sequence {\n"
+"  addAll(other) {\n"
+"    for (element in other) {\n"
+"      add(element)\n"
+"    }\n"
+"    return other\n"
+"  }\n"
+"\n"
 "  toString {\n"
 "    var result = \"[\"\n"
 "    for (i in 0...count) {\n"