Implement a `where` method on the List class that takes a predicate function and returns a new list containing only elements for which the predicate returns true. The implementation iterates over the list, calls the predicate on each element, and collects matching elements into a new list. Includes test cases verifying filtering with both matching and non-matching predicates.
Add `+` method to List class in core.wren that creates a new list by concatenating elements from both operands. Supports concatenation with Range objects and handles empty lists on either side. Includes comprehensive test cases in test/list/concat.wren covering list-list, list-range, and empty list combinations.