[TRTLLM-6577][feat] Support nano_v2_vlm in pytorch backend

* clean up codes.
* add test_e2e for nano_v2 vlm.

Signed-off-by: Wanli Jiang <35160485+Wanli-Jiang@users.noreply.github.com>

Author: Wanli-Jiang

tensorrt_llm/_torch/models/modeling_nanov2vlm.py

@@ -1,3 +1,4 @@
+# Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved.
 import copy
 import os
 from typing import List, Optional, Tuple
@@ -279,6 +280,11 @@ def __call__(
                     Image.fromarray((image.permute(1, 2, 0) * 255).to(
                         torch.uint8).cpu().numpy()) for image in images
                 ]
+        else:
+            input_ids = self.tokenizer.encode(text_prompt,
+                                              add_special_tokens=False,
+                                              return_tensors="pt")
+            return input_ids[0].to(torch.int32).tolist(), {}
 
         # Processing for multimodal data.
         processed_images = self.processor(images=images,