Add option to use highest quality version of cover instead of 1200x1200 cover

[jcomicsutils]

Is your feature request related to a problem? Please describe.
Not a problem.

Describe the solution you'd like
A new option to use the highest quality of a cover art (the one ending with _0 instead of any other number) instead of the 1200x1200 version.

Describe alternatives you've considered
Downloading each manually.

Additional context
I don't think that'd be hard to implement, since it already fetches the cover, all it'd need to do is change the final two numbers (covernumber_##.jpg) to 0 (covernumber_0.jpg).

[Evolution0]

Had to check because its been so long since touching on this code but yeah seems like just changing the number to 0 defaults to whatever the source image is on their backend.

I can't default to that however, there are some considerations to be made for when a user is embedding the album art into each track with --embed-art as it would inflate file sizes without good reason. I could possibly add options to --embed-art to choose between full, half, and quarter res though and just have the unembedded cover file being max res.

[Evolution0]

Looking deeper into this starting with a cover image that is 3000x3000:

0  = max (3000, Source?)
1  = max (3000, Source?)
2  = 350x350
3  = 300x300
4  = 300x300
5  = 700x700
6  = 100x100
7  = 150x150
8  = 124x124
9  = 210x210
10 = 1200x1200 (Album page cover, default)
11 = 172x172
12 = 138x138
13 = 380x380
14 = 368x368
15 = 135x135
16 = 700x700
17 = Invalid
18 = Invalid
19 = Invalid
20 = 1024x1024
21 = 120x120
22 = 25x25
23 = 300x300
24 = 300x300
25 = 700x700
26 = 800x600
27 = 715x402
28 = 768x432
29 = 100x75
30 = Invalid
31 = 1024x1024
32 = 380x285
33 = 368x276
34 = Invalid
35 = Invalid
36 = 400x300
37 = 168x126
38 = 144x108
39 = Invalid
40 = Invalid
41 = Invalid
42 = 210x210
42 = 50x50
43 = 100x100
44 = 200x200
45 = Invalid
46 = Invalid
47 = Invalid
48 = Invalid
49 = Invalid
50 = 140x140
51+ = Invalid

The images also seem to be PNG not JPG as the path would suggest, not sure if its a quirk of the image server or what. The reason I needed to know what resolutions are available is I do not want to introduce any additional requirements (like Pillow) just to be able to add this functionality so I may just work with what resolutions the image backend has available as show above.

Likely this will mean 3000x3000, 1200x1200, 1024x1024, and 700x700.

[jcomicsutils]

The _0 variant can be either png or jpg (or even animated GIF really), it depends on what the artist uploaded. Embedding the high quality cover to each file really is too much, but being able to have it saved as a file would be great.

[jcomicsutils]

Also, since this is about cover art, some albums have tracks with different cover art than the album, this one for example: https://standby-band.bandcamp.com/album/we-need-more-mountains-i. Maybe there could be a key to check for the track cover art url, and if it's different than the album art url it saves that file as well? In the given example the album cover url is https://f4.bcbits.com/img/a2556534090_10.jpg, for track 1, that has a different cover art, the url is https://f4.bcbits.com/img/a2915853457_10.jpg, but track 3 has the same cover as the album, and the url is https://f4.bcbits.com/img/a2556534090_10.jpg, same as the album. So it seems like a simple check could save the different covers.

[Evolution0]

Worth looking into, in the mean time the current codebase will download the highest quality cover, it also embeds it as-is though if --embed-art is used so be aware of that, I still need to add an option to switch resolutions.

Leaving this open till I feel the solution for handle album art is "complete".