Implemented `starknet_getClassAt` and `starknet_getClassHashAt` #24

Job	Run time
Enforce CHANGELOG / changelog	3s
Verify configs / Verify genesis-assets hashes	7s
Verify configs / Genesis documentation	0s
Build & Integration Tests	0s
Run linters	0s
Test Madara commands	0s
Run Starknet Foundry compatibility tests	0s
Run Cargo linters	0s
Run starknet-js compatibility tests	0s
Run rpc tests	0s
	10s

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