use custom VoteState parser everywhere

[2501babe]

Problem

earlier this year we implemented VoteState::deserialize_into(), a custom parser intended to be suitable for usage in a bpf context. we want to use the new parser everywhere because, with some optimizations, it is 7-20x faster than bincode depending on the input

HANA custom vs bincode
* we win: 10000, they win: 0
* our max 22.422µs, their max 471.89µs
* our avg 5.76µs, their avg 35.956µs
* avg speedup 30.195µs

it also uses half as much memory for V1_14_11 because conversion to Current happens during parsing

Summary of Changes

use VoteState::deserialize_into() as the new implementation for VoteState::deserialize(). we also remove the check for prior_voters sparsity that wouldnt exist in bincode and remove unnecessary uses of serialized_size() which drastically improve runtime

this wont be merged immediately. the plan is to cherrypick the new parser into a 2.x codebase and run that as a validator on mainnet for a few epochs to confirm everything works identically, because it is impossible to feature-gate this change

the hope is enough vote parsing happens that this will have a nontrivial performance improvement, but that is something to figure out how to measure

fixes solana-labs#35101

[2501babe]

new plan is to split this in half, merge the deserialize_into fixes now, and delay replacing deserialize until later, so that deserialize_into can be used to optimize vote processing