Add command to view the download cache

[goodmami]

Is your feature request related to a problem? Please describe.

There is no good way to view and clean up the cache. There is wn.config.get_cache_path(), but it's not convenient as one would need to know the URL.

Describe the solution you'd like

Something like this:

$ python -m wn cache
0f5371187dcfe7e05f2a93ab85b4e1168859a5c2  oewn:2025+  https://en-word.net/...
e25af66e46775b00d689619787013e6a35e5cbf7  oewn:2025   https://en-word.net/...
3aef6bc5b31087b768bc7d40a9f2963cfe03dc9c  omw:2.0     https://github.com/...
[...]
$ python -m wn cache oewn:2022
3e786e15b7f43627beddafdfa4a95807a5b12cf7  oewn:2022   https://en-word.net/...
c89ce73144c15fce143ee766c73fbd14e86bb71c  oewn:2022   https://github.com/...
$ python -m wn cache oewn:2022 --clear -v
Removing 3e786e15b7f43627beddafdfa4a95807a5b12cf7
Removing c89ce73144c15fce143ee766c73fbd14e86bb71c
2 cache entries removed

These commands would likely be backed by some public API Python functions.

[goodmami]

I'm removing the intention to have a --clear option to avoid creating an attack mechanism like getting people to type:

$ python -m wn --dir=~/ cache --clear

... which could start deleting files in someone's home directory (well, ~/downloads/ at least).

Instead, maybe have an option to print the full paths only, so people can do something like:

$ python -m wn cache --paths-only | xargs rm

I'm also thinking about cache entries that don't have a corresponding index entry (e.g., from downloading from an unindexed URL). For these, we can't get a project specifier or a URL. We could attempt to open it with wn.project.get_project() to automatically decompress, untar, etc., then get access to READMEs and resource files. This creates the decompressed files under /tmp/, and it is slower, so it should only be done with some option, like --inspect or maybe -vv.