Comprehensive snapshot verification

[mmcgee-jump]

See Agave equivalent, e.g. all the codes like

pub enum VerifySlotDeltasError {
    #[error("too many entries: {0} (max: {1})")]
    TooManyEntries(usize, usize),

    #[error("slot {0} is not a root")]
    SlotIsNotRoot(Slot),