Function start_pproxy_server 

pub async fn start_pproxy_server(protocol: &str, port: u16) -> ProcessGuard

Start a pproxy server with the given protocol and port.

Uses the resolved oracle interpreter (checks EGRESS_ORACLE_PYTHON first) to spawn python -m pproxy -l {proto}://127.0.0.1:{port} -r direct. Returns a ProcessGuard that kills the process on drop.