Add statement interruption support

This adds an interrupt() method to Statement that allows apps to
interrupt a running statement. Please note that this is different from
`sqlite3_interrupt()` which interrupts all ongoing operations in a
database. Although we want to support that too, per statement interrupt
is much more useful to apps.

bindings/python/src/lib.rs

@@ -134,6 +134,9 @@ impl Cursor {
                             PyErr::new::<OperationalError, _>(format!("IO error: {:?}", e))
                         })?;
                     }
+                    limbo_core::RowResult::Interrupt => {
+                        return Ok(None);
+                    }
                     limbo_core::RowResult::Done => {
                         return Ok(None);
                     }
@@ -165,6 +168,9 @@ impl Cursor {
                             PyErr::new::<OperationalError, _>(format!("IO error: {:?}", e))
                         })?;
                     }
+                    limbo_core::RowResult::Interrupt => {
+                        return Ok(results);
+                    }
                     limbo_core::RowResult::Done => {
                         return Ok(results);
                     }