BUG: min_level and max_level are not reliably set

[matthewturk]

Some of the handlers are not correctly setting max_level, which then propagates to things like ds.r[:]. For instance:

import yt
import numpy as np
oct_mask = np.zeros(33)
oct_mask[[0,  5,  7, 16]] = 8
octree_mask = np.array(oct_mask, dtype=np.uint8)
quantities = {}
quantities["gas", "density"] = np.random.random((29, 1))
bbox = np.array([[-10.0, 10.0], [-10.0, 10.0], [-10.0, 10.0]])

ds_octree = yt.load_octree(
        octree_mask=octree_mask,
        data=quantities,
        bbox=bbox,
        num_zones=1,
        partial_coverage=0,
)
#ds_octree.max_level = 10

print(ds_octree.r[:]["ones"])

This does not actually return anything! The array is empty, because the _selector that is created has a max_level that it inherits from the ds_octree, which is set to 0. Setting it to any value at or greater than the maximum level will work to get all the values.

This is kind of a big deal I think, and probably worth being a blocker. I don't know when this was introduced.