Avoid runtime allocations

[bonnee]

The error subsystem relies on llist to store errors ordered by priority. This is problematic because llist uses dynamic allocations at runtime. With this method an insert operation is O(n) and a removal is O(1) (with the help of an array that stores the index of allocations).

To replace llist it would be adequate to find a solution that is at least as efficient as llist is now. min-heap seems to be a good candidate if paired with list_ref.

While runtime memory allocation is not ideal, it doesn't affect my sleep too much, so this issue is not really an urgent one.