Abstract over the various data types needed by the consensus engine

[romac]

Closes: #11

This gist of this PR is that it adds a Consensus trait which defines the various datatypes that the consensus engine operates over, as well as a trait per such datatype that defines the requirement for said datatype.

pub trait Consensus
where
    Self: Sized,
{
    type Address: Address;
    type Height: Height;
    type Proposal: Proposal<Self>;
    type PublicKey: PublicKey;
    type Validator: Validator<Self>;
    type ValidatorSet: ValidatorSet<Self>;
    type Value: Value;
    type Vote: Vote<Self>;

pub trait Height
where
    Self: Clone + Debug + PartialEq + Eq + PartialOrd + Ord,
{
}

etc.

In test code, we define our own simple versions of these datatypes as well as a TestConsensus struct, for which we implement the Consensus trait.

#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
pub struct Address(u64);

impl Address {
    pub const fn new(value: u64) -> Self {
        Self(value)
    }
}

impl malachite_common::Address for Address {}

pub struct TestConsensus;

impl Consensus for TestConsensus {
    type Address = Address;
    type Height = Height;
    type Proposal = Proposal;
    type PublicKey = PublicKey;
    type ValidatorSet = ValidatorSet;
    type Validator = Validator;
    type Value = Value;
    type Vote = Vote;
}

[codecov]

Codecov Report

Merging #8 (5909cf1) into romac/rust-state-machine (ccc12e6) will decrease coverage by 2.48%.
The diff coverage is 88.14%.

@@                     Coverage Diff                      @@
##           romac/rust-state-machine       #8      +/-   ##
============================================================
- Coverage                     85.60%   83.12%   -2.48%     
============================================================
  Files                            15       17       +2     
  Lines                          1007      794     -213     
============================================================
- Hits                            862      660     -202     
+ Misses                          145      134      -11     

Files	Coverage Δ
Code/common/src/vote.rs	100.00% <ø> (ø)
Code/round/src/events.rs	100.00% <ø> (ø)
Code/round/src/state.rs	98.39% <100.00%> (+0.31%)	⬆️
Code/test/src/proposal.rs	100.00% <100.00%> (ø)
Code/test/src/vote.rs	100.00% <100.00%> (ø)
Code/vote/src/lib.rs	92.86% <100.00%> (ø)
Code/common/src/round.rs	92.00% <90.91%> (+10.00%)	⬆️
Code/test/src/consensus.rs	90.00% <90.00%> (ø)
Code/vote/src/count.rs	80.65% <90.00%> (-9.60%)	⬇️
Code/vote/src/keeper.rs	65.91% <80.00%> (-21.01%)	⬇️
... and 7 more

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[romac]

I have also been experimenting with finer-grained generics instead of stuffing everything into a single Consensus trait, but it’s getting very convoluted and pretty hairy.

It’s possible that I am going at this the wrong way but so far I would be in favor of keeping the Consensus trait rather than have finer-grained generics.

[romac]

Drop in coverage is likely because a bunch of code was moved to the test crate, ie. deleted from the main crates and added to the test crate.