zfs: add ZFS "topology" features like explicit vdevs, cache, and special

[dmadisetti]

Addresses vdev definitions, partially addressing #298

I don't think this is the most elegant solution, so happy to churn over this a few times. Happy to receive feedback.
TODOs as I see it:

• More comprehensive tests, currently just a stub
• Clean up. I'm not exceptionally happy with this and would love some feedback, but I tried to stick the spec in ZFS features support #298

I think it might be worth having a lib/types/zfs folder. The vdev submodule could then be moved to be a standalone file without polluting the diskoTypes. Might be worth doing in another PR.

stakeholders: @victorklos @nbraud @luishfonseca @Mic92 @Lassulus

[victorklos]

How very nice that you are working on this! Glad to confirm your code is working and allowed me to use disko on a previously unsupported ZFS layout.

A couple of things remain, of which one is critical: the members of a vdev can either be whole disks or partitions.

Are you interested in feedback on a broader usability/logical level, or is your goal to produce something that is usable? Just asking before I get carried away ;)

[dmadisetti]

Thanks @victorklos ! This was more so that I could utilize Disko myself in a similar "hack it together" context.

I would like a potential refactor and before upstreaming though.

I would love some feedback, maybe in the context of the comments that @ Mic92 has already left. I think they are good suggestions, I just haven't gotten around to it

[0x450x6c]

LUKS support would be nice.

[dmadisetti]

Addressed comments, and pulled in commit from @0x450x6c

I can clean up the commit history, but seems like everything gets merged anyway ¯\(ツ)/¯

[Mic92]

Looks overall pretty good.

[dmadisetti]

Checks are not deterministic locally, and I cannot reliably cause them to intentionally fail.

I'm OK with what's here, there is more work to be done to support all vdevs, and I think some of the edgecase tests can be picked up with that.

As such, taking off draft