Remove pymoab as a Dependency

[ahnaf-tahmid-chowdhury]

Description

This PR removes pymoab from pyproject.toml as a dependency.

Changes

Here are the main changes made in this PR:

1. pyproject.toml: Removed pymoab from the list of dependencies.

2. dagnav.py: Added instructions to handle the case if pymoab is not found.

[pshriwise]

I know I suggested this in #1, but the message is a overly verbose for my taste. There are (somewhat dated) instructions on how to build MOAB with PyMOAB enabled here. I think we should point to them in this message and update the installation instructions there.

Also, while we may want to add a logging capability to this project in the future, I don't see the point of importing that module for this single message. We can raise our own message from a ModuleNotFoundError

try:
    from pymoab import core, types, rng, tag
except ImportError as e:
    msg = 'PyMOAB package was not found, please install this package using the instructions found here: https://ftp.mcs.anl.gov/pub/fathom/moab-docs/building.html'
    raise ModuleNotFoundError(msg) from e

[pshriwise]

A couple of comments form me, but I think this is close!

[gonuke]

LGTM - I'll let @pshriwise decide if it's ready