Particle visual size vs. collision size

[kno10]

Problem

Particle textures may be next to transparent on the outer pixels.
However, collision code uses a bounding box around the particle of +-size/2:

luanti/src/client/particles.cpp

Line 93 in abcd2e0

aabb3f box(v3f(-m_p.size / 2.0f), v3f(m_p.size / 2.0f));

Solutions

It may be good to allow adding a multiplier here (because size may be randomized, a factor may be better), i.e., allow specifying collision_size_factor = 0.5.

Alternatives

Specify collision size in absolute values, e.g., mod devs might use minsize=6, maxsize=8, collision_size=4.

Additional context

E.g., smoke particles from campfires clearly should have collisions, but with collisions may have a hard time passing through a chimney node.