fix(schema): restore static return type on Table::index() for fluent chaining

Agent-Logs-Url: https://github.com/utopia-php/query/sessions/5b098851-2af2-49e9-8778-d7edb0172860

Co-authored-by: abnegate <5857008+abnegate@users.noreply.github.com>

Author: Copilot

src/Query/Schema/Table.php

@@ -373,7 +373,7 @@ public function index(
         ?IndexAlgorithm $algorithm = null,
         array $algorithmArgs = [],
         int $granularity = 1,
-    ): void {
+    ): static {
         if ($name === '') {
             $name = $this->autoIndexName('idx_', $columns);
         }
@@ -390,6 +390,8 @@ public function index(
             algorithmArgs: $algorithmArgs,
             granularity: $granularity,
         );
+
+        return $this;
     }
 
     /**