Hi,
I had errors loading "*so" files, such as "libLinearMath.so".
To make it possible to use BulletCollision, I had to change this line

so_hdr = "/usr/local/lib"

which solved the problem.

BulletCollision.distance(BulletCollision.convex_hull([
            [0.0; 0.0; 0.0], 
            [4.0; 0.0; 0.0],
            [4.0; 4.0; 0.0],
            [0.0; 4.0; 0.0]
            ]), 
    BulletCollision.convex_hull([
            [3.0; 1.0; 0.0], 
            [5.0; 1.0; 0.0],
            [5.0; 3.0; 0.0],
            [3.0; 3.0; 0.0]
            ]))

Result:
(-0.0f0, Float32[4.0, 0.0, 0.0], Float32[4.0, 0.0, 0.0])
From your implementation, it seems like it should compute the penetration depth as well, but it merely returns 0.0 distance.
Do you have any idea why this happens? Is it a degenerative case for EPA? If yes, how to avoid this?