[feat] Add contract types like in other SDKs

[ClementWalter]

In starknet-py or starknet-js, one can use the Contract class, especially Contract.from_address to have a high level human-readable interaction with contracts. For example, one can do

starknet_eth = Contract.from_address(provider, 0x49...)
await starknet_eth.balance_of(0x1234)

or also build such an object from an embedded abi object.

Currently with starknet-rs, we end up doing encoding and decoding manually with raw starknet call/invoke. Or I am missing something?

[xJonathanLEI]

ABI-based encoding/decoding is indeed one more the most important missing features in starknet-rs. Will prioritize this accordingly.