[RPC] Support finalized tag

We are currently ignoring the BlockTag, and always return the latest block ( best block) stored in the cache.

https://github.com/paritytech/polkadot-sdk/blob/2f65b31a0dd38c2bdbda2905793f85a4207cf2d7/substrate/frame/revive/rpc/src/client.rs?plain=1#L616-L630

We should update code that uses BlockTag to make sure that handle the Finalized tag