fix: convert UploadFile to bytes for File() parameter validation

- Added UploadFile-to-bytes conversion in _normalize_field_value()
- Handles type annotations including Annotated[bytes, File()]
- Fixes 24 failing tests in test_file_parameter.py
- All tests now return 200 OK instead of 422 validation errors

Resolves multipart form data parsing issue where UploadFile instances
weren't being converted to bytes before Pydantic validation.

Author: oyiz-michael

aws_lambda_powertools/event_handler/middlewares/openapi_validation.py

@@ -597,6 +597,21 @@ def _handle_missing_field_value(
 
 def _normalize_field_value(value: Any, field_info: FieldInfo) -> Any:
     """Normalize field value, converting lists to single values for non-sequence fields."""
+    # Convert UploadFile to bytes if the expected type is bytes
+    if isinstance(value, UploadFile):
+        # Check if the annotation is bytes
+        annotation = field_info.annotation
+        # Handle Annotated types by unwrapping
+        if hasattr(annotation, "__origin__"):
+            from typing import get_args
+
+            args = get_args(annotation)
+            if args:
+                annotation = args[0]
+
+        if annotation is bytes:
+            return value.file
+
     if field_annotation_is_sequence(field_info.annotation):
         return value
     elif isinstance(value, list) and value: