Add example of moving across TX types / RLP serialization

[zerosnacks]

Add example of moving across the different TX types / RLP serialization for usage in i.e. Flashbots

From Telegram / Discord:

How can I go from a TxEnvelope to a more usable one like alloy_rpc_types::Transaction or similar? AFAIK TxEnvelope is the only type we're supposed to use when RLP decoding raw bytes

Users may want to serialize their things as RLP for usage in flashbots where they put a signed rlp transactions behind a txhash

regular users should only interact with TransactionRequest and TransactionEnvelope. they should never RLP anything

you should never decode raw rlp bytes, you should decode raw 2718 bytes. going from TxEnvelope to rpc::Transaction is not possible because rpc::Transaction contains more information