Rename the first batch of "sources" to "models"

[jeremykubica]

This is the first PR in solving #418. Changes a bunch of the classes with source in the name to model. Also changes MultiSourceModel to MultiObjectModel

[review-notebook-app]

Check out this pull request on 

See visual diffs & provide feedback on Jupyter Notebooks.

---

Powered by ReviewNB

[codecov]

Codecov Report

❌ Patch coverage is 94.23077% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.50%. Comparing base (c87cfd4) to head (4b61a64).
⚠️ Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
src/tdastro/sources/multi_object_model.py	92.85%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #423   +/-   ##
=======================================
  Coverage   91.50%   91.50%           
=======================================
  Files          53       53           
  Lines        3767     3767           
=======================================
  Hits         3447     3447           
  Misses        320      320           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

Before [e411ac4]	After [70fd228]	Ratio	Benchmark (Parameter)
failed	33.3±0.2ms	n/a	benchmarks.TimeSuite.time_additive_multi_model_source
failed	1.37±0.07ms	n/a	benchmarks.TimeSuite.time_apply_passbands
failed	7.65±0.2ms	n/a	benchmarks.TimeSuite.time_apply_white_noise
failed	19.0±0.3ms	n/a	benchmarks.TimeSuite.time_chained_evaluate_sed
failed	9.52±0.3ms	n/a	benchmarks.TimeSuite.time_evaluate_salt3_model
failed	4.96±0.2ms	n/a	benchmarks.TimeSuite.time_evaluate_salt3_passbands
failed	119±10μs	n/a	benchmarks.TimeSuite.time_evaluate_simple_linear_wavelength_model
failed	677±9μs	n/a	benchmarks.TimeSuite.time_fnu_to_flam
failed	4.66±0.03ms	n/a	benchmarks.TimeSuite.time_lightcurve_source
failed	8.37±0.05ms	n/a	benchmarks.TimeSuite.time_load_passbands

Click here to view all benchmarks.

[olivialynn]

Submitting my current comments to avoid losing them; I've gone through all .py files and am about to begin .ipynb files

[olivialynn]

Looks good!