Cleanup rpc pkg

[rianhughes]

Currently there is a lot of duplicated code in the rpc v6, v7 and v8 sub packages. We should remove duplicated code (types, functions, tests) where possible. For example, the blockHashAndNumber function (and associated type BlockHashAndNumber) has not changed between v6, v7 and v8. This means that we can remove this function (and type) from v7 and v8, and have the top level handler use the code in v6 instead (specifically update the MethodsV0_8 and MethodsV0_7 functions). See this PR as an example. We should do this for all RPC methods. I would suggest doing the following:

1. Create a PR for each RPC method (this will make it easier to track changes, work on, and review)
2. If the RPC method has not changed between (eg) v6, v7 and v8, then we can just re-use the v6 code in v7 and v8. This means the corresponding code (function, types, tests) should be deleted in v7 and v8.
3. If the RPC function has changed, then we should not remove the function. However, if the associated type has not changed, then we should probably delete it.
4. To keep track of all the changes being made, and still to be made, to the RPC pkg, please add a new bullet point here and link the associated PR.

• starknet_chainId
• starknet_blockNumber
• starknet_blockHashAndNumber
• BlockStatus enum (Not really an RPC endpoint but useful for other endpoints, such as starknet_getBlockWithTxHashes)
• Header struct (Not really an RPC endpoint but useful for other endpoints, such as starknet_getBlockWithTxHashes)
• starknet_getBlockWithTxHashes
• Refactor type Transaction struct (Not really an RPC endpoint but useful for other endpoints)
• starknet_syncing
• starknet_getNonce
• starknet_getClassAt
• starknet_getClassHashAt
• starknet_getClass
• starknet_getEvents
• juno_version
• starknet_getStorageProof
• starknet_getTransactionByHash
• starknet_getTransactionCount
• starknet_getStateUpdate
• starknet_call
• starknet_estimateMessageFee
• juno/starknet_unsubscribe
• starknet_add...Transaction
• starknet_traceTransaction

Remaining endpoints to check

• starknet_getBlockWithReceipts
• starknet_getCompiledCasm
• starknet_specVersion
• starknet_subscribeEvents
• starknet_subscribeTransactionStatus
• starknet_getBlockWithTxs
• starknet_getTransactionByHash
• starknet_getTransactionReceipt
• starknet_getBlockTransactionCount
• starknet_getTransactionByBlockIdAndIndex
• starknet_getStateUpdate
• starknet_addInvokeTransaction
• starknet_addDeployAccountTransaction
• starknet_addDeclareTransaction
• starknet_getTransactionStatus
• starknet_call
• starknet_estimateFee
• starknet_estimateMessageFee
• starknet_traceTransaction --> decided not to go for refactoring after all. Not exactly straightfoward.
• starknet_simulateTransactions
• starknet_traceBlockTransactions
• juno_subscribeNewHeads / starknet_subscribeNewHeads
• juno_unsubscribe / starknet_unsubscribe