Cascade support on terms with variables

[farnoy]

Describe the bug
Cascade ordering doesn't seem to be working with a relationship pair

To Reproduce

use flecs_ecs::prelude::*;

#[derive(Component, Debug)]
struct MyData {
    data: u32,
}

fn main() {
    let mut world = World::new();
    let e1 = world.entity_named("e1").set(MyData { data: 1 });
    let e3 = world.entity_named("e3").set(MyData { data: 3 });
    let e2 = world.entity_named("e2").set(MyData { data: 2 }).child_of_id(e1);
    let e4 = world.entity_named("e4").set(MyData { data: 4 }).child_of_id(e3);
    e3.child_of_id(e2);
    // e1 -> e2 -> e3 -> e4

    let q = world
        .query::<()>()
        .with::<&MyData>()
        .with::<&flecs::ChildOf>()
        .set_second_name("$loc")
        .src()
        .cascade()
        .desc()
        .self_()
        .optional()
        .set_cached()
        .build();
    println!("{}", q.to_string());
    println!("{}", q.plan());
    q.each_iter(|e, index, ()| unsafe {
        println!("[{index}] = {} parent {}", e.entity(index).name(), e.get_var_by_name("loc").name());
    });
}

Actual output

[in] ecs_tests.MyData($this), [in] ?ChildOf($this|self|cascade|desc ChildOf,$loc)
 0. [-1,  1]  setids
 1. [ 0,  2]  cachepop
 2. [ 1,  4]  option
 3. [ 2,  4]   selfup     $[this]           (ChildOf, $loc)
 4. [ 2,  5]  end         $[this]           (ChildOf, $loc)
 5. [ 4,  6]  yield

[0] = e1 parent *
[0] = e2 parent e1
[0] = e4 parent e3
[0] = e3 parent e2

Seems like no sorting is done and it matches physical/insertion order.

Expected behavior
I expected to see a descending cascade with this output:

[0] = e4 parent e3
[0] = e3 parent e2
[0] = e2 parent e1
[0] = e1 parent *

Additional context
I want to pull more than one component out of the traversal target. Cascade queries require caching, which only supports a single cascade traversal. Is this not a good alternative? I wanted to do ?OtherData($loc), ?SomethingElse($loc) once I got this working

[SanderMertens]

This requires being able to cache terms that have variables, which is something I hope to look into soon.

I wanted to do ?OtherData($loc), ?SomethingElse($loc) once I got this working

That should work!