Handle Flint plot info with `redis-om`

For #20, I plan to heavily change the Flint plotting.

This MR is the first step to help me understand the code better. My idea was to

1. Improve the robustness of the code by using stronger typing for the plot info (replacing the dict with a redis-om Model).
2. Refactor a bit to improve the readability of the code: rename some functions, remove some that were breaking the flow in my opinion

I can continue but I'll stop for now. Next steps I envision:

• Abstract the memory (data_key) vs HDF5 data fetching (hdf5_url). We can probably get away by using a single address that can be resolved to Redis or HDF5.
• Decouple the plot info creation from the plotter to accommodate for 2d intergation data