[UX] Add progress bar for diffusion models

[gcanlin]

PLEASE FILL IN THE PR DESCRIPTION HERE ENSURING ALL CHECKLIST ITEMS (AT THE BOTTOM) HAVE BEEN CONSIDERED.

Purpose

When models are generating very long video/image, the program looks like being stuck and makes users confused. We should add a bar for better UX.

Test Plan

 python text_to_image.py \
  --model Qwen/Qwen-Image \
  --prompt "a cup of coffee on the table" \
  --seed 42 \
  --cfg-scale 4.0 \
  --num-images-per-prompt 1 \
  --num-inference-steps 50 \
  --height 1024 \
  --width 1024 \
  --output outputs/coffee.png

Test Result

============================================================
Generation Configuration:
  Model: Qwen/Qwen-Image
  Inference steps: 50
  Cache backend: None (no acceleration)
  Quantization: None (BF16)
  Parallel configuration: tensor_parallel_size=1, ulysses_degree=1, ring_degree=1, cfg_parallel_size=1, vae_patch_parallel_size=1
  CPU offload: False
  Image size: 1024x1024
============================================================

Adding requests:   0%|                                                                                                  | 0/1 [00:00<?, ?it/s[Stage-0] INFO 03-04 08:24:35 [manager.py:566] Deactivating all adapters: 0 layers?, ?it/s, est. speed input: 0.00 unit/s, output: 0.00 unit/s]
[Stage-0] WARNING 03-04 08:24:35 [kv_transfer_manager.py:421] No connector available for receiving KV cache
100%|█████████████████████████████████████████████████████████████████████████████████████████████████████████| 50/50 [00:17<00:00,  2.92it/s]
[Stage-0] INFO 03-04 08:24:52 [diffusion_engine.py:80] Generation completed successfully.
[Stage-0] INFO 03-04 08:24:52 [diffusion_engine.py:98] Post-processing completed in 0.0576 seconds
Processed prompts: 100%|███████████████████████████████████| 1/1 [00:17<00:00, 17.55s/img, est. speed stage-0 img/s: 0.00, avg e2e_lat: 0.0ms]
Adding requests:   0%|                                                                                                  | 0/1 [00:17<?, ?it/s]
Total generation time: 17.5603 seconds (17560.27 ms)
INFO 03-04 08:24:52 [text_to_image.py:401] Outputs: [OmniRequestOutput(request_id='', finished=True, stage_id=0, final_output_type='image', request_output=[OmniRequestOutput(request_id='0_86f585a2-e797-4de5-bcd0-85ecc7108456', finished=True, stage_id=None, final_output_type='image', request_output=None, images=[1 PIL Images], prompt={'prompt': 'a cup of coffee on the table', 'negative_prompt': None, 'additional_information': {'global_request_id': ['0_86f585a2-e797-4de5-bcd0-85ecc7108456']}}, latents=None, metrics={'image_num': 1, 'resolution': 640, 'postprocess_time_ms': 57.55615234375}, multimodal_output={})], images=[], prompt=None, latents=None, metrics={}, multimodal_output={})]
Saved generated image to outputs/coffee.png

============================================================
Generation Configuration:
  Model: Wan-AI/Wan2.2-TI2V-5B-Diffusers
  Inference steps: 40
  Frames: 33
  Parallel configuration: ulysses_degree=1, ring_degree=1, cfg_parallel_size=1, tensor_parallel_size=1, vae_patch_parallel_size=1
  Video size: 832x480
============================================================

Adding requests:   0%|                                                                                                  | 0/1 [00:00<?, ?it/s[Stage-0] INFO 03-04 08:49:15 [diffusion_engine.py:75] Pre-processing completed in 0.0000 secondsspeed input: 0.00 unit/s, output: 0.00 unit/s]
[Stage-0] INFO 03-04 08:49:15 [manager.py:592] Deactivating all adapters: 0 layers
[Stage-0] WARNING 03-04 08:49:15 [kv_transfer_manager.py:421] No connector available for receiving KV cache
 60%|███████████████████████████████████████████████████████████████                                          | 24/40 [00:08<00:05,  2.74it/s

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan. Please provide the test scripts & test commands. Please state the reasons if your codes don't require additional test scripts. For test file guidelines, please check the test style doc
• The test results. Please paste the results comparison before and after, or the e2e results.
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model. Please run mkdocs serve to sync the documentation editions to ./docs.
• (Optional) Release notes update. If your change is user-facing, please update the release notes draft.

BEFORE SUBMITTING, PLEASE READ https://github.com/vllm-project/vllm-omni/blob/main/CONTRIBUTING.md (anything written below this line will be removed by GitHub Actions)

[gcanlin]

Only add with self.progress_bar(total=len(timesteps)) as pbar: for this changing block.

[gcanlin]

cc @hsliuustc0106 @princepride @ZJY0516

[lishunyang12]

Looks good. Nit: PR title says "process bar" — should be "progress bar".

[gcanlin]

Looks good. Nit: PR title says "process bar" — should be "progress bar".

Thanks for pointing out the typo :)

[lishunyang12]

Thanks for spoting this issue. This PR is very helpful to improve user experience. Sometimes, I also have the same confusion withthe long generation time with no cues and warning messages constantly poping up.

[hsliuustc0106]

lgtm