feat: add a to.(device) method for the BoxUniform prior

[janfb]

[jorobledo]

This branch attempts to add a to(device) to BoxUniform

https://github.com/jorobledo/sbi/tree/device

This is the relevant commit

I thought of two solutions and added a test in the tests folder tests/device_test.py.

There is an inplace replacemente method .to(device and also another option which is ._to(device), which is not inplace, but needs to be assigned to a new variable. Something like

prior = prior._to(device)

instead of

prior.to(device)

The thing is that in the tests, the assignment method samples way faster than the inplace option (both show a speedup in comparison to "cpu"). Tested it on mps device and gpu.

What do you think?

[janfb]

fixed with #1505