Create a MIST interpolation interface, replace isochrones

[TomWagg]

This pull request introduces significant improvements to the handling of photometric calculations in the codebase, focusing on the integration and use of MIST bolometric correction grids. The main changes include the addition of a new module for managing MIST bolometric corrections, updates to the photometry interface to support more flexible and modern filter naming, and general modernization and cleanup of dependencies and imports. These changes improve both the scientific accuracy and the usability of the code when working with stellar populations and their observable properties.

Photometry and Observables Modernization:

• Added a new module cogsworth/obs/mist.py implementing the MISTBolometricCorrectionGrid class, which handles downloading, caching, and interpolating MIST bolometric correction grids for a wide range of photometric systems and bands. This replaces the previous dependency on the external isochrones package for this functionality.
• Updated the get_photometry function (now in cogsworth/obs/observables.py) to use the new MISTBolometricCorrectionGrid class, added parameters for specifying the main filter and silencing out-of-bounds warnings, and improved handling of filter naming and interpolation. [1] [2] [3] [4] [5]
• Changed default filter names throughout the codebase to use modern, explicit names (e.g., "Gaia_G_EDR3" instead of "G"), including in the plot_cmd function and get_gaia_observed_bin_nums method. [1] [2] [3]

Code Organization and Import Updates:

• Renamed the observables.py module to obs/observables.py and updated all imports to reflect this new structure, improving code organization and clarity. [1] [2]

Infrastructure and Dependency Updates:

• Added caching of MIST data in the GitHub Actions workflow to speed up CI runs.
• Updated the Python version used in documentation builds from 3.10 to 3.11 and removed a now-unnecessary install step for the isochrones package, reflecting the new internal handling of bolometric corrections.

Versioning:

• Bumped the package version from 3.5.1 to 3.6.0 to reflect these substantial changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.90%. Comparing base (d210790) to head (f9c6006).
⚠️ Report is 21 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #184      +/-   ##
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- Coverage   100.00%   99.90%   -0.10%     
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  Files           15       16       +1     
  Lines         2077     2208     +131     
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+ Hits          2077     2206     +129     
- Misses           0        2       +2     

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PS: if you wanted to spin this new code off into a new small package, I know some people who would use it!!