fix: Raise if list.concat is called on a non list column

[gab23r]

Closes the concat part of #25649
list.concat() wasn't ensuring the input was a list. This is fixed.

Why the PR is more complicated:

• list.concat() and concat_list() shared the same code path (ListFunction::Concat)
• We needed list.concat() to require list input (and fail early on non-list columns)
• But concat_list() must continue to accept non-list columns (it wraps them into lists)

Now two different paths exists:

The Solution - Two Separate Paths:

1. *list.concat() uses ListFunction::Concat and we use mapper.ensure_is_list()...
2. concat_list()uses FunctionExpr::ConcatList, this can takes any inputs.

I used AI for all the boilerplate