It renames poseidon to halo2_poseidon, I think that makes more sense to import halo2_poseidon::poseidon::* than poseidon::poseidon::*, also prefixing with halo2_ is somehow ortogonal to our way to define crates in halo2
Fixes benches ( removes sinsemilla bench leftover, also )
Updates toolchain with the minimum version requiered ( mainly for ahash )
This PR fixes some stuff:
poseidontohalo2_poseidon, I think that makes more sense to importhalo2_poseidon::poseidon::*thanposeidon::poseidon::*, also prefixing withhalo2_is somehow ortogonal to our way to define crates in halo2