Update State.store to be able to store multiple key-values

[iFrostizz]

As raised in #1095 (comment)
The current way of putting stuff in storage is by calling store on the state directly which takes as an input a K: Key, V: BorshSerialize. This is problematic if there is a lot of data to store because we need to call the function independently multiple times which takes a lot of code space.
We should create a function that allows storing a list of tuple (K, V) in storage.