TransactionCost::SimpleVote doesn't report correct number of sigs for two-sig votes

[steviez]

Problem

TransactionCost has two cases in the enum; SimpleVote and Transaction. A SimpleVote is defined by these things:

agave/cost-model/src/transaction_cost.rs

Lines 8 to 10 in 11aa06d

	/// SimpleVote has a simpler and pre-determined format: it has 1 or 2 signatures,
	/// 2 write locks, a vote instruction and less than 32k (page size) accounts to load.
	/// It's cost therefore can be static #33269.

Note that a SimpleVote can contain 1 or 2 signatures, but TransactionCost::num_transaction_signatures() reports a fixed value of 1 for simple votes:

agave/cost-model/src/transaction_cost.rs

Lines 95 to 100 in 11aa06d

	pub fn num_transaction_signatures(&self) -> u64 {
	match self {
	Self::SimpleVote { .. } => 1,
	Self::Transaction(usage_cost) => usage_cost.num_transaction_signatures,
	}
	}

This doesn't affect actual fees (the fee-payer will still be charged for 2 sigs) or CU's in the way things are currently written, but for the sake of accurate counting, it is incorrect.

Proposed Solution

Update SimpleVote to track the number of signatures:

agave/cost-model/src/transaction_cost.rs

Line 15 in 11aa06d

SimpleVote { writable_accounts: Vec<Pubkey> },

and populate that field here:

agave/cost-model/src/cost_model.rs

Lines 40 to 42 in 11aa06d

	TransactionCost::SimpleVote {
	writable_accounts: Self::get_writable_accounts(transaction),
	}

[steviez]

Not super high priority to fix at the moment, one of us will pick it up eventually

[apfitzge]

Just want to clarify here for later - transactions are still charged the correct fee, for 2 signatures, it is just not properly accounted for by cost-model.