PosProof should be parametrized by K

[dariolina]

Currently value for SIZE includes a hardcoded to 20 in PosProof:

subspace/crates/subspace-core-primitives/src/lib.rs

Line 236 in 047479c

pub const SIZE: usize = 20 * 8;

But should depend on this K:

subspace/crates/subspace-proof-of-space/src/chia.rs

Line 7 in 6d1043b

const K: u8 = 20;

I also suspect there may be a better place for K as well

[nazar-pc]

Primitives are primitives, they should not depend on heavy PoSpace implementation.
Also parametrizing it by K while possible, has far reaching consequences and currently code base is not ready for K to ever change. While those constants are in different places, code will fail to compile if they mismatch, so in that context it should not be a huge problem that they are in different places, but we can definitely move it to core primitives if necessary, there was just no use for it.

I saw discussions about K change, is that something we expect we may need? I thought we settled on 20 quite some time ago.

[dariolina]

The expectation for K was that it should be possible to change after launch if we deem 20 no longer adequate as the computational capabilities of hardware increase. I am aware that current implementation doesn't fully support (though a lot of it does, like table generation) that, so opened this issue to start steering it on the right track.