cleanup

- fix some warnings and mark others as expected
- make use of the msrv bump to 1.93.1 and cleanup compat and workarounds

src/arena.rs

@@ -13,6 +13,8 @@ use ordered_float::OrderedFloat;
 use std::fmt;
 use std::fmt::Debug;
 use std::hash::{Hash, Hasher};
+use std::io::PipeReader;
+use std::io::PipeWriter;
 use std::mem;
 use std::mem::ManuallyDrop;
 use std::net::TcpListener;
@@ -22,8 +24,6 @@ use std::ptr;
 use std::ptr::addr_of_mut;
 use std::ptr::NonNull;
 
-use crate::machine::streams::{PipeReader, PipeWriter};
-
 macro_rules! arena_alloc {
     ($e:expr, $arena:expr) => {{
         let result = $e;