feat: Introduce on the fly attributes reordering with meilidb-core

meilidb-core/src/reordered_attrs.rs

@@ -0,0 +1,20 @@
+#[derive(Default)]
+pub struct ReorderedAttrs {
+    count: usize,
+    reorders: Vec<Option<u16>>,
+}
+
+impl ReorderedAttrs {
+    pub fn insert_attribute(&mut self, attribute: u16) {
+        self.reorders.resize(attribute as usize + 1, None);
+        self.reorders[attribute as usize] = Some(self.count as u16);
+        self.count += 1;
+    }
+
+    pub fn get(&self, attribute: u16) -> Option<u16> {
+        match self.reorders.get(attribute as usize) {
+            Some(Some(attribute)) => Some(*attribute),
+            _ => None,
+        }
+    }
+}