docs: improve assert() message to clarify its purpose

Added descriptive message to assert(class_exists($className)) to explain:
- This is an internal logic error, not invalid user input
- $className comes from ReflectionParameter type info, so it should always exist
- assert() is the appropriate tool for checking "impossible" conditions
- Can be disabled in production for performance, unlike explicit exceptions

This addresses code review concerns about assert() usage while maintaining
the correct semantic distinction between internal logic errors (assert)
and user input validation (exceptions).

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: koriym

src/InputQuery.php

@@ -265,7 +265,8 @@ private function resolveObjectType(ReflectionParameter $param, array $query, arr
 
         // Check if the parameter name exists as a direct nested array in query
         if (array_key_exists($paramName, $query) && is_array($query[$paramName])) {
-            assert(class_exists($className));
+            // This should never fail as $className comes from ReflectionParameter type info
+            assert(class_exists($className), "Internal logic error: Class '$className' from reflection should exist");
 
             /** @var Query $nestedQuery */
             $nestedQuery = $query[$paramName];