This PR makes all the StoredAccountMeta fields pub(crate)
and provides getter functions to access its member fields.
This PR is a preparation step for abstracting out StoredAccountMeta.
#### Problem
As we start supporting new storage formats, those account-meta
structs will be shared by different storage formats and thus need
a new home.
#### Summary of Changes
This PR creates meta.rs under account_storage and moves all the account-meta
structs out from append_vec.rs.
#### Current implementation of ReplicaAccountInfo restricts
possibilities for inflight account filtration
Current implementation includes transaction signature in
ReplicaAccountInfo. This approach does not allow to filter accounts by
matching other accounts in transaction in-flight (e. g. accept only
those accounts included in transactions for specific programs). Current
implementation forces to collect ALL accounts and transactions for some
period of time and perform such complex filtration afterwards.
#### Pass reference to transaction object instead of transaction
signature into ReplicaAccountInfo
Advanced in-flight filtration can be implemented in plugins by passing
reference to transaction for every update_account event. This change
doesn't bring any overhead comparing to current implementation (only
data type of reference is changed) and brings only minor changes in
source code.
There's no direct linkage between account-update events and transaction-events
Issue is linked with geyser plugin interface
Currently, there's no straightforward way to determine what notify_transaction call is related to particular update_account call. So, there's no simple way to determine what transaction caused what changes in accounts. This issue is especially valuable in case when several transactions modifies single account in the same slot.
Add txn_signature field to ReplicaTransactionInfo structure
This additional field will contain the signature of transaction which caused this account update event. This modification is not bringing significant overhead because all necessary information for such linkage already available inside Accounts::collect_accounts_to_store method