Summary of the charges in a transaction.
Storage is charged independently of computation.
There are 3 parts to the storage charges:
storage_cost: it is the charge of storage at the time the transaction is executed.
The cost of storage is the number of bytes of the objects being mutated
multiplied by a variable storage cost per byte
storage_rebate: this is the amount a user gets back when manipulating an object.
The storage_rebate is the storage_cost for an object minus fees.
non_refundable_storage_fee: not all the value of the object storage cost is
given back to user and there is a small fraction that
is kept by the system. This value tracks that charge.