Improve Isotope Instantiation

[tjlaboss]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

"I'm always frustrated when" I want to instantiate an Isotope, but have to remember that it lives at montepy.data_inputs.isotope.Isotope. It should be a top-level object.

Also annoying is that the representation uses the "Element-Z" convention, but instantiation has to use ZAID.

Example

>>> montepy.data_inputs.isotope.Isotope("1001.00c")
Isotope('H-1.00c')

>>> Isotope('H-1.00c')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'Isotope' is not defined

>>> montepy.data_inputs.isotope.Isotope("H-1.00c")
Traceback (most recent call last):
  File "montepy/data_inputs/isotope.py", line 34, in __init__
    int(parts[0])
ValueError: invalid literal for int() with base 10: 'H-1'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "montepy/data_inputs/isotope.py", line 36, in __init__
    raise ValueError(f"ZAID: {ZAID} could not be parsed as a valid isotope")
ValueError: ZAID: H-1.00c could not be parsed as a valid isotope

Describe the solution you'd like

• Import the Isotope class into the top-level namespace, in montepy/init.py
• Allow instantiation from, e.g., montepy.Isotope("H-1.00c"), montepy.Isotope("H1.01c"), etc.

Additional context
Someone changed the repr in #473, but didn't bother to update __init__ accordingly.

[MicahGale]

See the initial function over on mat_redesign. Also get_from_fancy_name. Now in #507

[MicahGale]

Side note: montepy.particle.Particle is annoying. I think we need to make basically everything a top level object. At the very least module.Class for particle.Particle is really annoying.

[tjlaboss]

Yes.