Add a 2D VolBlock equivalent

[nicopap]

Closes #27

Note the get_column impl block is commented out because
it requires unstable features. Though in practice, get_row is
the most important.

[Lokathor]

Looks like you'll maybe have to raise the CI MSRV some? I'm shocked that we didn't already have a panic in a const fn somewhere in the crate, but maybe we only ever had const-if instead.

[nicopap]

Looks like const_panic was stabilized on 1.57, just one version short of the voladdress current MSRV, let's see if bumping it works rust-lang/rust#89508

[Lokathor]

I released voladdress-1.1, which adds a small method for converting addresses of arrays into blocks, but also includes this PR behind another "experimental" flag. I suspect things are totally fine, but I'd rather have it be opt-in for a while just in case.

[nicopap]

Thank you for the blazing fast response and merge. I wasn't expecting such velocity.