[#10029][benchmarks] arrow-flight roundtrip as well as encode/decode

[Rich-T-kid]

Which issue does this PR close?

• Contributes towards closing Optimize arrow-flight #10029.

Rationale for this change

Provides benchmarks for arrow-flight crate. benchmarks for round trip as well as encode/decode individually.

What changes are included in this PR?

Adds three criterion benches under arrow-flight/benchmarks/ (roundtrip.rs, flight_encode.rs, flight_decode.rs), each sweeping a tunable matrix of rows, cols, and column types (fixed Int64, variable StringArray, nested List, dict DictionaryArray) built via a shared
common::build_batch helper.

Are these changes tested?

n/a

Are there any user-facing changes?

no

[Rich-T-kid]

@alamb could you take a look at this when you get a chance? smaller PR that only includes benchmarks, #10029 has a bit more context. 🫡

[gabotechs]

👍 nice work @Rich-T-kid! pretty clean benchmarks. Left some suggestions, but otherwise this LGTM

[gabotechs]

+1 to skipping formatting here, otherwise this boilerplaty code occupies too much space.

[gabotechs]

Actually, rather than spawning a real server in local-host, you may want to spawn a fully in-memory server here. That way sys calls to the network interface of the OS are not baked into the benchmarks.

[gabotechs]

Something like this should be the same thing, but the everything is spawned in-memory, without passing through localhost:

pub async fn start_server() -> (Channel, BenchServer) {
    const DUMMY_URL: &str = "http://localhost:50051";

    let bench_server = BenchServer::default();

    let (client, server) = tokio::io::duplex(1024 * 1024);

    let mut client = Some(client);
    let channel = Endpoint::try_from(DUMMY_URL)
        .expect("Invalid dummy URL for building an endpoint. This should never happen")
        .connect_with_connector_lazy(tower::service_fn(move |_| {
            let client = client
                .take()
                .expect("Client taken twice. This should never happen");
            async move { Ok::<_, std::io::Error>(TokioIo::new(client)) }
        }));
    tokio::spawn(
        Server::builder()
            .add_service(FlightServiceServer::new(bench_server.clone()))
            .serve_with_incoming(tokio_stream::once(Ok::<_, std::io::Error>(server))),
    );
    (channel, bench_server)
}

[gabotechs]

Typically, the folders containing benchmarks are not called benchmarks, they are instead called benches.

Can we rename the folder containing this code to account for this?