Add ELBDM/UniformGranule test problem

[HsunYeong]

Add a test problem to simulate periodic box with homogeneous FDM granule initial condition.

[vivi235711]

Hi, I left some comments here.

[vivi235711]

Hi. I left some comment here.
Because I'm not familiar with the correlation function, could you please share the reference about how to calculate it? I confused why divided by std^2 or mean^2.

[vivi235711]

I only have one minor comment.

[ChunYen-Chen]

@HsunYeong
Could you update the download link of the uniform-granule.tar.gz according to gamer-project#390? I have uploaded uniform-granule.tar.gz to ythub. The link to uniform-granule.tar.gz is

https://hub.yt/api/v1/item/677cc1c3999605c485c8de80/download

An example of the download script:

#!/bin/bash

LOCAL_FILENAME="uniform-granule"
FILE_ID="677cc1c3999605c485c8de80"

# 1. download
curl https://hub.yt/api/v1/item/${FILE_ID}/download -o "${LOCAL_FILENAME}.tar.gz"

# 2. unzip
tar -zxvf ${LOCAL_FILENAME}.tar.gz
rm ${LOCAL_FILENAME}.tar.gz

See also gamer-project#408.

[hyschive]

@HsunYeong Thanks for the contribution! I've added some comments, mostly regarding wording and formatting.

The only major suggestion is to file a separate PR to add support for computing standard deviation in Aux_ComputeProfile.cpp.

Additionally, please merge the latest psidm branch.