Use `taxa.py` functions to handle taxonomic information instead of custom logic

[bruvellu]

The logic for querying, adding, and handling taxonomic information from WoRMS exists since March 2023 via update_taxa.py management command. I adapted this code into a general library named taxa.py with the goal of making these functions reusable for the new dashboard. However, the current taxonomic handling is running a custom logic using the low-level worms.py functions (see #296). There are differences in how the ancestor tree is fetched and how valid taxa are identified. In addition, the media from invalid taxa are not assigned to the correspondent valid taxa. This code needs to be revised and refactored to use taxa.py. I haven't tested extensively, but I'll paste some bugs I found below.