Adds the blob test to examples/HydroTests/BlobTest_3D
This MR adds the infamous blob test from Agertz+2007.
It includes a moving making script, IC script, and a readme.
Here's how various SWIFT schemes perform at high resolution:
I could probably work more on this but I think we're at the 80% stage here, and the improvements are required more on the swiftsimio side.
Edited by Josh Borrow