Add hydro submodule for creating populations from hydrodynamical zoom-in simulations

[TomWagg]

Rather a large PR here. Copying from the docs:

The hydro module contains the functionality necessary for running simulations that use hydrodynamical
zoom-in simulations as their initial conditions. This includes the ability to read in snapshots,
centre and rotate them, estimate the galactic potential, get the initial conditions of star particles and
run a full cogsworth Population based on all that!

Tutorials and tests are still to come but it seems to work for now! This will fix #92 and will fix #93.

The _tohspans function is my personal favourite addition 😜

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
1434	1310	91%	0%	🟢

New Files

File	Coverage	Status
cogsworth/hydro/init.py	100%	🟢
cogsworth/hydro/pop.py	17%	🟢
cogsworth/hydro/potential.py	29%	🟢
cogsworth/hydro/rewind.py	29%	🟢
cogsworth/hydro/test.py	0%	🟢
cogsworth/hydro/utils.py	40%	🟢
TOTAL	36%	🟢

Modified Files

File	Coverage	Status
cogsworth/citations.py	100%	🟢
cogsworth/pop.py	100%	🟢
TOTAL	100%	🟢

updated for commit: 265680c by action🐍