Replace critnib with a RAVL tree to track allocations in providers

This is a rough idea - I'm not 100% sure that this solution will not have any disadvantages.

Currently, on every split or merge, we add and remove entries from critnib structures to track allocations at various levels. This proposal suggests replacing those structures with a RAVL tree instead.

A key advantage of using a RAVL tree is the ability to search for a key that is equal to or lower than a specified value. After a split, this feature allows reusing the original entry in the tree, eliminating the need to update it. As a result, overall performance is improved by reducing the overhead of frequent insertions and deletions. In addition, a RAVL tree will be smaller, which further enhances search times.

Start by locating the provider allocation-tracking code that currently uses critnib structures, then review how split and merge operations add and remove entries. Evaluate whether a RAVL tree supports the proposed lower-or-equal-key lookup without introducing disadvantages. Done means a justified implementation or decision, with performance and correctness validated for allocation tracking.