Model xklb-metadata.db using SQLAlchemy

[deldesir]

This pull request aims to model the xklb-metadata.db database using SQLAlchemy to manage media, captions, and playlists information. The new models provide a structured way to interact with the database and support operations such as creating, updating, and querying media and related data.

• Tested on Ubuntu 24.04

[holta]

1. What are the fundamental reasons that a blank xklb-metadata.db is (allegedly) needed?

   • Thanks @deldesir for explaining this apparently quite fundamental question!
   • As I'm not understanding yet why this is suddenly (claimed?) to be an urgent priority. 😉

2. Would this PR be intended to partially replace one-or-both below... ?

   • PR New xb.py: Possible schema to standardize xklb db's + main operations? [need to align w/ Calibre-Web's metadata.db & app.db!] #253
   • PR Begin with blank xklb-metadata.db from template? [w/ key columns added for Calibre-Web videos] iiab#3808

[deldesir]

1. What are the fundamental reasons that a blank xklb-metadata.db is (allegedly) needed?

   • Thanks @deldesir for explaining this apparently quite fundamental question!
   • As I'm not understanding yet why this is suddenly (claimed?) to be an urgent priority. 😉

2. Would this PR be intended to partially replace one-or-both below... ?

   • PR New xb.py: Possible schema to standardize xklb db's + main operations? [need to align w/ Calibre-Web's metadata.db & app.db!] #253
   • PR Begin with blank xklb-metadata.db from template? [w/ key columns added for Calibre-Web videos] iiab#3808

This PR does not create a blank database anymore. As explained in the description, it does one thing, modeling xklb-metadata.db. It is based on the experimental PR New xb.py: Possible schema to standardize xklb db's + main operations? [need to align w/ Calibre-Web's metadata.db & app.db!] #253. As for the reason behind creating a blank, it was for convenience. A db with all key columns would prevent missing columns error and avoid the need to add them (altering the db).

PR Begin with blank xklb-metadata.db from template? [w/ key columns added for Calibre-Web videos] iiab#3808 is not relevant anymore, see PR Add xklb-patch script iiab#3827.

[deldesir]

How to test

• Pull the PR following How do I test a pull request (PR) ? instructions.
• Before downloading a video, do ls /library/calibre-web/xklb-metadata.db in your terminal to check for the db existence. If it exists, that means the SQLAlchemy successfully created it, attesting the effectiveness of the database modeling.