fix bbox planar intersection

[AhmetNSimsek]

This PR fixes the no intersection issue when the intersection of 2 bounding boxes is planar and hence have volume 0 resulting in None. This meant that while there are some intersections, these were ignored. Also, the edge case, the intersection is just a point, is accounted for.

code to reproduce the issue on current main

import siibra
points = siibra.PointSet(
    [
        [-35.72, -1.87, 35.03],
        [-33.7, -1.87, 36.2],
        [-32.56, -1.87, 34.34],
        [-35.62, -1.87, 35.2],
    ],
    "bigbrain",
)
matched_sections = siibra.features.get(
    points, siibra.features.cellular.CellbodyStainedSection
)
assert len(matched_sections) > 0
voi = points.boundingbox

# this is expected to fetch but fails assuming there is no intersection
patch_1mu = matched_sections[0].fetch(voi=voi, resolution_mm=-1)

[xgui3783]

LGTM, but you should check with @dickscheid to see if volume check is important.

remind me, restrict_space=False is the default for siibra.features.get() right?

This issue does not affect siibra python v2, since there is no volume check.

[AhmetNSimsek]

LGTM, but you should check with @dickscheid to see if volume check is important.

There is a conversation about it here. I thought I remembered all the details but I will make some adjustments to this PR based on Timo's comment.

remind me, restrict_space=False is the default for siibra.features.get() right?

Yes by default it is false, i.e., compares anchors across different spaces.

This issue does not affect siibra python v2, since there is no volume check.

True