Merge 'implement Clone for Arc<Mutex> types' from Pete Hayman

`Statement` and `Rows` both have a private Arc, implementing clone
avoids users needing to Arc<Mutex> it again.

Reviewed-by: Preston Thorpe (@PThorpe92)

Closes #1412

bindings/rust/src/lib.rs

@@ -129,6 +129,14 @@ pub struct Statement {
     inner: Arc<Mutex<limbo_core::Statement>>,
 }
 
+impl Clone for Statement {
+    fn clone(&self) -> Self {
+        Self {
+            inner: Arc::clone(&self.inner),
+        }
+    }
+}
+
 unsafe impl Send for Statement {}
 unsafe impl Sync for Statement {}
 
@@ -241,6 +249,14 @@ pub struct Rows {
     inner: Arc<Mutex<limbo_core::Statement>>,
 }
 
+impl Clone for Rows {
+    fn clone(&self) -> Self {
+        Self {
+            inner: Arc::clone(&self.inner),
+        }
+    }
+}
+
 unsafe impl Send for Rows {}
 unsafe impl Sync for Rows {}
 
@@ -281,4 +297,8 @@ impl Row {
             limbo_core::OwnedValue::Blob(items) => Ok(Value::Blob(items.to_vec())),
         }
     }
+
+    pub fn column_count(&self) -> usize {
+        self.values.len()
+    }
 }