Newly created accounts should not be looked up on disk

### Problem

`StakingRewardsHandlerImpl.getStakedToMeRewardReceivers()` calls `getOriginalValue(id)` for all accounts modified in the current transactions. If the transaction creates a new account, that new account will be found neither in `ReadableKVStateBase`'s cache nor by `readFromDataSource(id)`. The latter, however, involves a disk read which is expensive. At high TPS and large scale it takes ~50% of transaction handling.

### Solution

Add newly created accounts to `ReadableKVStateBase`'s cache?
Avoid that code path for newly created accounts?

### Alternatives

_No response_

Start by tracing StakingRewardsHandlerImpl.getStakedToMeRewardReceivers() and its getOriginalValue(id) calls into ReadableKVStateBase. Determine how newly created accounts are represented during the current transaction, then verify that those accounts no longer trigger readFromDataSource(id) while existing-account lookups retain their behavior.

Written by the indexing model from the issue text.