proxyd: support `eth_sendRawTransactionSync`

See discussion [here](https://ethresear.ch/t/halving-transaction-submission-latency-with-eth-sendrawtransactionsync/22482), but the tldr is that this cuts the number of networking roundtrips down when submitting a transaction, decreasing the latency of tx confirmation in particular for chains that have fast blocktimes.

It has been merged into geth in https://github.com/ethereum/go-ethereum/pull/32830. There is viem support for this method, would be good to have strong support in OP Stack and have applications start migrating to it to decrease latency

The issue names proxyd but no file, test, or entry point. Read the linked ethresear.ch discussion and geth PR first, then locate proxyd's handling of JSON-RPC methods; done means OP Stack supports eth_sendRawTransactionSync for lower-latency transaction submission.

Written by the indexing model from the issue text.