feat: suspend managed calls on generic awaitable operands

crates/objects/src/error.rs

@@ -4,6 +4,8 @@ use std::fmt;
 /// retained for embedders; defining it here avoids a dependency on the VM.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum VmError {
+    AwaitFailed(String),
+    AwaitCancelled,
     ForeignHandle,
     InvalidHandle,
     IdentityExhausted,
@@ -49,6 +51,8 @@ pub enum VmError {
 impl fmt::Display for VmError {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
+            Self::AwaitFailed(message) => write!(f, "await failed: {message}"),
+            Self::AwaitCancelled => f.write_str("await cancelled"),
             Self::ForeignHandle => f.write_str("handle belongs to another VM"),
             Self::InvalidHandle => f.write_str("handle does not identify a live object"),
             Self::IdentityExhausted => f.write_str("process-local VM identities exhausted"),