refactor(client): replace mio with tokio

- Use `tokio` instead of `mio`.
- Refactor `neqo-client` to be more consistent with `neqo-server`.
  - Introduce `read_datagram` and `ready`.
  - Introduce `ClientRunner` and `old::ClientRunner` (consistent with `ServersRunner`).
- Fold `handle_test` into `client` (now `ClientRunner::new`).

neqo-client/Cargo.toml

@@ -9,14 +9,16 @@ rust-version = "1.70.0"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
-mio = "~0.6.23"
+futures = "0.3"
+log = {version = "0.4.17", default-features = false}
 neqo-common = { path="./../neqo-common" }
 neqo-crypto = { path = "./../neqo-crypto" }
 neqo-http3 = { path = "./../neqo-http3" }
 neqo-qpack = { path = "./../neqo-qpack" }
 neqo-transport = { path = "./../neqo-transport" }
 qlog = "0.11.0"
 structopt = "0.3"
+tokio = { version = "1", features = ["net", "time", "macros", "rt", "rt-multi-thread"] }
 url = "~2.5.0"
 
 [features]