Add distributed PoSt API

[cryptonemo]

Relies on filecoin-project/rust-fil-proofs#1283 and filecoin-project/rust-filecoin-proofs-api#41

This work does NOT yet include the proofs.go updates required. I will look at that next unless @magik6k or @Kubuxu can get to it quicker.

@dignifiedquire This may have issues, but I fixed the specific nastiness I was fighting earlier.

[cryptonemo]

Hrm, I don't understand the CI darwin error and didn't locally get the clippy warning, but can look at tomorrow. Fixed

[vmx]

@nemo You need to run clippy with the -all-targets flag. The CI runs clippy --all-targets --all-features -- -D warnings

[cryptonemo]

Wow, this CI took forever but passed! Still missing is the glue in proofs.go that wrap the new calls. Anyone want to help there?

[cryptonemo]

@magik6k or @Kubuxu Would either of you guys be able to provide the proofs.go glue to do the final wiring to the newly generated methods? I honestly think it should be painless, but it's taking me too long struggling with the go side (just don't know it, and banging around isn't working).

[cryptonemo]

Nice work, thanks @Kubuxu!

[Kubuxu]

@cryptonemo this is done as far as go side goes.

[cryptonemo]

@Kubuxu This tests well here. I think we are good to go on both sides now! @porcuquine or @dignifiedquire for final approval?

[dignifiedquire]

while the above works, it should be safer and less error prone to do

let slice: &[u8] = unsafe { std::slice::from_raw_parts(self.proof_ptr, self.proof_len) };
let cloned: Vec<u8> = slice.to_vec();
debug_assert_eq!(self.proof_len, cloned.len());

let proof_ptr = cloned.as_ptr();
mem::forget(cloned);

fil_VanillaProof {
  proof_len: self.proof_len,
  proof_ptr,
}

this way it is guranteed that reconstructing this will actually work as expected

[dignifiedquire]

one comment, other than that looks good to me