Tried adding option to insert arbitrary model

[Takatho]

Adressing issue #37

[MetinSa]

Looks nice, good job! I will make some slight edits and add some units tests and then we are ready for a merge :)

[MetinSa]

To test that the code works remember to follow the instruction in the README, specifically by running pytest, ruff and mypy as instructed. I will modify the code to make sure the tests and linting is happy:)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (38a3e8a) to head (f8e6bad).
Report is 68 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main       #38      +/-   ##
===========================================
+ Coverage   98.76%   100.00%   +1.23%     
===========================================
  Files          19        14       -5     
  Lines         807       708      -99     
===========================================
- Hits          797       708      -89     
+ Misses         10         0      -10     

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[MetinSa]

Good addition to ZodiPy as it allows for visualization and gridding of custom non-registered models. Initial state did not pass tests and were not formatted. This is now fixed and the PR is ready to be merged.

[MetinSa]

@Takatho if you take a look at the changes ive made, the argument name is now replaced with model to better reflect the two new possible types. Make sure to change this in your code!