feat(rpc): trivial methods using new serialization trait

[Mirko-von-Leipzig]

Implements some of the simpler RPC methods using the new trait.

Note that this explicly targets RPC v0.7-rc2 only. No backwards compatibility yet - let's fully support v0.7 and then we can work backwards. This let's us skip work for v0.4 and v0.5 if we manage to remove them before this work gets there.

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Particular review focus should be on the correctness of the DTO serialization ito inner types being used. i.e. ensure that if the spec says BLOCK_HASH is a FELT then the serialization implementation should use serialize(&Felt(...)).

There isn't really a super easy way to enforce this apart from rigorous manual auditing when adding/updating DTOs.

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Adds DTO implementations for:

FELT
BLOCK_HASH
BLOCK_NUMBER
SYNC_STATUS
CHAIN_ID

and implements methods

starknet_blockHashAndNumber
starknet_blockNumber
starknet_chainId
starknet_syncing

Part of #1830

[kkovaacs]

LGTM, except for the dbg!() @sistemd already pointed out.