Remove ptr-int transmute in std::sync::mpsc
Since https://github.com/rust-lang/rust/pull/95340 landed, Miri with `-Zmiri-check-number-validity` produces an error on the test suites of some crates which implement concurrency tools<sup>*</sup>, because it seems like such crates tend to use `std::sync::mpsc` in their tests. This fixes the problem by storing pointer bytes in a pointer.
<sup>*</sup> I have so far seen errors in the test suites of `once_cell`, `parking_lot`, and `crossbeam-utils`.
(just updating the list for fun, idk)
Also `threadpool`, `async-lock`, `futures-timer`, `fragile`, `scoped_threadpool`, `procfs`, `slog-async`, `scheduled-thread-pool`, `tokio-threadpool`, `mac`, `futures-cpupool`, `ntest`, `actix`, `zbus`, `jsonrpc-client-transports`, `fail`, `libp2p-gossipsub`, `parity-send-wrapper`, `async-broadcast,` `libp2p-relay`, `http-client`, `mockito`, `simple-mutex`, `surf`, `pollster`, and `pulse`. Then I turned the bot off.
7af93292c2