docs: document client public API

crates/irtt-client/src/managed/cancellation.rs

@@ -3,20 +3,31 @@ use std::sync::{
     Arc,
 };
 
+/// Cloneable cooperative cancellation flag.
+///
+/// Managed sessions use this internally to ask their worker loop to stop. It is
+/// exported for callers that want the same simple cancellation primitive in
+/// code built around `irtt-client`.
 #[derive(Debug, Clone, Default)]
 pub struct CancellationToken {
     cancelled: Arc<AtomicBool>,
 }
 
 impl CancellationToken {
+    /// Create a token in the non-cancelled state.
     pub fn new() -> Self {
         Self::default()
     }
 
+    /// Mark the token as cancelled.
+    ///
+    /// Cancellation is idempotent and is visible through all clones of the
+    /// token.
     pub fn cancel(&self) {
         self.cancelled.store(true, Ordering::SeqCst);
     }
 
+    /// Return whether cancellation has been requested.
     #[must_use]
     pub fn is_cancelled(&self) -> bool {
         self.cancelled.load(Ordering::SeqCst)