Handle contracts with duplicated names

[cptartur]

It is possible to have a compiling Scarb package containing contracts with duplicated names e.g.

src/
  lib.rs <- Contract named MyContract
tests/
  contracts.rs <- Contract named MyContract

In starknet_artifacts.json file they are correctly distinguished by their full paths and two .contract_class files are generated. However we have no logic to handle duplicated names and since we handle contract by names using a hashmap, which contract will be collected is undefined. This may result in different contracts being used between different tests runs.

We should introduce a logic to handle these duplicated entries and update the syntax of declare cheatcode:
If there is only one implementation under given <ContractName> allow declaring with declare(<ContractName>).
If there are duplicated names, require declaring with full path (declare(full::path::<ContractName>)) and fail otherwise (consider panic since it's a code error).