remove special case for 8M range covers

[mekarpeles]

Closes #9560 (at least for critical items in the 8M range).

This does not update the database -- the filename field is the only field which requires an update, but they are kept as is in case there's any need to use the existing tar offsets. The zip filenames are automatically inferred by the cover id.

The following script can be used to generate db statements if we want to update the filename field:

x = 10_000
for i in range(100):
     p = str(i).zfill(2)
     print(f"update cover set filename='covers_0008/covers_0008_{p}.zip' where id >={str(8_000_000 + (i * x))} and id < { str(8_000_000 + ((i+1) * x))};")

For the purpose of doing this in a non-breaking way, I've already added a field to the coverstore.cover table called filename_old which equals the current value of filename so if anything were to go wrong, we could overwrite filename with filename_old. After this work is completed, we likely want to delete the filename_old column as it takes up necessary space for the ~1M covers where these values have been backed up.

Technical

Testing

Screenshot

Stakeholders

[cdrini]

Lgtm one small change then feel free to merge 👍 Tested these covers work:

http://covers.openlibrary.org/b/id/8000001-S.jpg
http://covers.openlibrary.org/b/id/8000001-M.jpg
http://covers.openlibrary.org/b/id/8000001-L.jpg
http://covers.openlibrary.org/b/id/8000001.jpg
http://covers.openlibrary.org/b/id/14000001-L.jpg