Many performance and memory optimizations

- Avoiding a memory copy on all socket reads and writes using a new `copy_from_slice` instead
- File openers no longer box the implementation avoiding a memory allocation on all file access
- Polling sockets rather than using an async function which significantly reduces locking contention and removes an box operation
- Futex now uses wakers rather than broadcasts which makes them more efficient and durable
- Converted many async functions into sync functions in vnet
- Sleeping no longer allocates memory
- Avoiding a number of WasiEnv clones which was impacting performance and memory efficiency

lib/api/src/js/mem_access.rs

@@ -311,6 +311,17 @@ impl<'a, T: ValueType> WasmSlice<'a, T> {
         self.buffer.write(self.offset, bytes)
     }
 
+    /// Reads this `WasmSlice` into a `slice`.
+    #[inline]
+    pub fn read_to_slice<'b>(
+        self,
+        buf: &'b mut [MaybeUninit<u8>],
+    ) -> Result<usize, MemoryAccessError> {
+        let len = self.len.try_into().expect("WasmSlice length overflow");
+        self.buffer.read_uninit(self.offset, buf)?;
+        Ok(len)
+    }
+
     /// Reads this `WasmSlice` into a `Vec`.
     #[inline]
     pub fn read_to_vec(self) -> Result<Vec<T>, MemoryAccessError> {

lib/api/src/sys/mem_access.rs

@@ -313,6 +313,17 @@ impl<'a, T: ValueType> WasmSlice<'a, T> {
         self.buffer.write(self.offset, bytes)
     }
 
+    /// Reads this `WasmSlice` into a `slice`.
+    #[inline]
+    pub fn copy_to_slice<'b>(
+        self,
+        buf: &'b mut [MaybeUninit<u8>],
+    ) -> Result<usize, MemoryAccessError> {
+        let len = self.len.try_into().expect("WasmSlice length overflow");
+        self.buffer.read_uninit(self.offset, buf)?;
+        Ok(len)
+    }
+
     /// Reads this `WasmSlice` into a `Vec`.
     #[inline]
     pub fn read_to_vec(self) -> Result<Vec<T>, MemoryAccessError> {