[RPCStateReader] Add support for executing Declare transactions (both versions)

[juanbono]

The main issues are:

• For Declare (v1) we need to fetch the contract class. This should be possible to do using the RPC or the feeder gateway.
• For DeclareV2. We need to find a way of bypassing the creation of a new DeclareV2 struct using a Sierra contract class since IIRC there is no RPC or feeder gateway endpoint for getting it. What we really need in the end is only the casm. So it should be possible to create a DeclareV2 without a Sierra class by adding another constructor and making some validation optional (depending on if there is a sierra contract class or not)