Add data() method to kqueue events (#772)

* Add data() method to kqueue events

This allows us to get the raw data field out, which is useful for reading
receipt events.

This lets us fully remove libc from polling, see this line:
https://github.com/smol-rs/polling/blob/6d13def8abd73da96d1e73090f490ae0ad36d6bd/src/kqueue.rs#L132

Signed-off-by: John Nunley <dev@notgull.net>

* Return i64 instead of isize

Signed-off-by: John Nunley <dev@notgull.net>

---------

Signed-off-by: John Nunley <dev@notgull.net>

src/event/kqueue.rs

@@ -99,6 +99,12 @@ impl Event {
         self.inner.udata as _
     }
 
+    /// Get the raw data for this event.
+    pub fn data(&self) -> i64 {
+        // On some bsds, data is an isize and not an i64
+        self.inner.data as _
+    }
+
     /// Get the filter of this event.
     pub fn filter(&self) -> EventFilter {
         match self.inner.filter as _ {