Implement ContractStorageDatabaseReadableKVState

[IvanKavaldzhiev]

Problem

We need to add a new type of database accessor to read contract storage, so that we have specific ReadableKVState instance for this type of data.

Solution

Add ContractStorageDatabaseReadableKVState class that reads contract storage related data and converts slotValue to SlotValue PBJ type.

Add unit tests to cover all cases including historical reads and correct mapping for all fields.

Alternatives

No response