fix: Transaction task use quorum exchange instead of committee exchange

[ggutoski]

close #1693

Change the transactions task to use quorum_exchange instead of committee_exchange so that VID can retrieve the number of storage nodes.

The VID erasure code rate is still hard-coded. That's a separate issue #1734 .

Other things in this PR beyond #1693

• Edit Committable impl for VIDBlockPayload to re-use the commitment bytes instead of computing another commitment of the commitment.
• Add test_memory_network to justfile.
• A few questions embedded in code comments. Search for TODO GG.

[shenkeyao]

LGTM. Thanks for adding those useful comments!

[shenkeyao]

Because we want to distinguish the vote type when signing, so a signature on a no vote can't be used to verify a yes vote.

[ggutoski]

But get_commit() just returns the underlying commitment regardless of the enum variant:

HotShot/crates/types/src/traits/election.rs

Lines 103 to 111 in 42d19ba

	pub fn get_commit(&self) -> COMMITMENT {
	#[allow(clippy::enum_glob_use)]
	use VoteData::*;
	match self {
	DA(c) | Yes(c) | No(c) | Timeout(c) | ViewSyncPreCommit(c) | ViewSyncCommit(c)
	| ViewSyncFinalize(c) => *c,
	}
	}
	}

Hmm. Seems it was me who made that change in #1777: https://github.com/EspressoSystems/HotShot/pull/1777/files

Ok, I need to fix this. I'll push more commits to this PR. Thanks for explaining!

[ggutoski]

fixed in 1fdc06a