Remove casatools dependencies from all examples

[iancze]

As has frequently been the case, the casatools Python package support lags the Python versions supported by SPEC 0. At time of writing, the newest version of Python supported by casatools is 3.10, which was deprecated by SPEC 0 in late 2022.

This creates a frustrating experience for MPoL users wishing to analyze ALMA data, where the dependence on casatools keeps them using an aging version of Python and prevents the installation of other packages requiring current versions of Python, and has led to several issues (#5 , #4 ).

As currently configured, to run successfully, each example folder requires at least two Python environments,

1. running Python no later than v3.10, to use casatools to extract the visibilities from a downloaded dataset (e.g., IM Lup, AS 209)
2. running Python that supports "minimum supported dependencies" as defined by SPEC 0 (currently 3.12 - 3.14), to run MPoL, PyTorch, etc.

This issue proposes decoupling these dependencies and isolating the Python 3.10 dependency to a single folder (00-download-datasets), where the user uses Python 3.10/casatools to extract the visibilities from the measurement set and save them in a .npz file.

Then, all subsequent examples (01, 02, ...) can use any of the modern SPEC 0 supported Python versions, simply reading the visibilities from the .npz file without any CASA dependency.

[iancze]

I suspect most users will have the same problem I have, which is that on my development machine, I have a single version of Python that I use for everything (e.g. 3.14), and I don't want to have to install/maintain a separate Python version just for this outdated task.

It seems like a neat solution is to create a Docker container with Python 3.10 and casatools installed and then upload that to the GitHub Container Registry. Then, in the 00 download and extract step, we can recommend that users just use our Docker container to execute the extraction.