Function read_storage_u64_be 

pub fn read_storage_u64_be<E, F: Fn(Address, B256) -> Result<Option<U256>, E>>(
    read_slot: &F,
    addr: Address,
    slot: B256,
) -> Result<Option<u64>, E>

Read a u64 from storage at a given slot (big-endian in last 8 bytes).

read_slot returns Ok(None) for an absent (zero) slot and Err for a backing-store failure; the error propagates so a failed read never silently reads as zero.