feat(proxyd): stream raw transactions over gRPC

[haardikk21]

Summary

• add the base.tx_ingress.v1.TransactionIngressService client contract from feat(tx-ingress): add streaming transaction submission base#4764
• optionally forward eth_sendRawTransaction to each backend's tx_ingress_endpoint over one persistent bidirectional gRPC stream
• correlate out-of-order stream responses with stream-local request IDs while preserving public JSON-RPC IDs and batch response order
• split mixed public JSON-RPC batches so raw transaction calls use the stream while other methods continue over HTTP
• reconnect after stream loss with request IDs reset for the new stream; existing proxyd retry and backend failover behavior remains in effect

rpc_url remains required for probes and all non-transaction methods. The stream is plaintext for use within the trusted VPC.

A transport failure can be ambiguous after a transaction has been sent. Existing proxyd retries may therefore resubmit it on a new stream or failover backend, as they can after an ambiguous HTTP failure; duplicate raw transactions remain identified by their transaction hash.

Depends on the receiver introduced by base/base#4764.

Testing

• go test ./...
• go test -race . -run TransactionIngress -count=1
• go vet ./...
• golangci-lint run -E goimports,sqlclosecheck,bodyclose,asciicheck,misspell,errorlint ... ./...

[haardikk21]

Closing because this is not the correct repository for the change.