Added PEP 723 metadata to download_deps.py (#4988)

### What problem does this PR solve?

Added PEP 723 metadata to download_deps.py

### Type of change

- [x] Refactoring

docs/guides/develop/build_docker_image.mdx

 ```bash
 git clone https://github.com/infiniflow/ragflow.git
 cd ragflow/
-pip3 install huggingface_hub nltk
-python3 download_deps.py
+uv run download_deps.py
 docker build -f Dockerfile.deps -t infiniflow/ragflow_deps .
 docker build -f Dockerfile -t infiniflow/ragflow:nightly .
 docker build --build-arg LIGHTEN=1 -f Dockerfile -t infiniflow/ragflow:nightly-slim .

download_deps.py

 #!/usr/bin/env python3
-#
-# Install this script's dependencies with pip3:
-# pip3 install huggingface-hub nltk
 
+# PEP 723 metadata
+# /// script
+# requires-python = ">=3.10"
+# dependencies = [
+#   "huggingface-hub",
+#   "nltk",
+# ]
+# ///
 
 from huggingface_hub import snapshot_download
 import nltk