dev: Use the AppchainCoreContract in the Starknet settlement client

[akhercha]

Follow-up from this issue: keep-starknet-strange/zaun#23

Current behavior

Due to incompatibilities with the usage of the Felt type from Zaun's implementation, we could not use this implementation in madara orchestrator.
At the moment, we are doing without it and just using the JsonProvider.

Expected behavior

After the migration has been done, the starknet settlement client should use the App chain core contract from Zaun and we should not call the provider, only use the contract provided interface.