iterators!

///ERROR:
 

  --> src/accounts.rs:196:9
    |
192 |     pub fn account_values_slow<R>(&self, fork: u64) -> R
    |                                                        - expected `R` because of return type
...
196 |         self.accounts.iter().map(|(k, v)| (fork, (k, v)))
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected type parameter, found struct 
`std::iter::Map`                                                                                      
    |
    = note: expected type `R`
               found type `std::iter::Map<hashbrown::map::Iter<'_, solana_
               
               
 ///CODE:
 
    pub fn account_values_slow<R>(&self, fork: u64) -> R
    where
        R: Iterator<Item = (u64, (Pubkey, solana_sdk::account::Account))>,
    {
        self.accounts.iter().map(|(k, v)| (fork, (k, v)))
    }