[RBTREE] Refactor `rb_*` APIs to Generic Naming for Future Flexibility
The current API set for range management is tightly coupled to the rbtree implementation, with function names prefixed as `rb_*`. 

However, the underlying data structure may evolve in the future.

To decouple the interface from the specific data structure and improve long-term maintainability, I propose renaming the `rb_*` APIs to use a more generic `range_*` prefix.

The proposed `range_*` prefix does not imply a change in implementation — it is simply an abstraction layer over the current `rbtree`. This naming can remain stable even if the underlying structure changes.

## Proposed Renaming

| Current Name           | Proposed Name         |
|------------------------|------------------------|
| `rbtree_init`          | `range_init`           |
| `rbtree_delet`         | `range_delete`         |
| `rb_get`               | `range_get`            |
| `rb_get_64`            | `range_get_64`         |
| `rb_get_end`           | `range_get_end`        |
| `rb_get_end_64`        | `range_get_end_64`     |
| `rb_set`               | `range_set`            |
| `rb_set_64`            | `range_set_64`         |
| `rb_unset`             | `range_unset`          |
| `rb_inc`               | `range_inc`            |
| `rb_dec`               | `range_dec`            |
| `rb_get_rightmost`     | `range_get_rightmost`  |
| `rb_get_leftmost`      | `range_get_leftmost`   |

Feel free to close this if it's not needed — I can submit a PR for this refactor if you think it's worthwhile.