Fix: switch Python package mirror from Tsinghua to Aliyun (#13617)

### What problem does this PR solve?

Replace pypi.tuna.tsinghua.edu.cn with mirrors.aliyun.com to resolve
issues with missing packages on the Tsinghua mirror.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Dockerfile

@@ -80,7 +80,7 @@ RUN --mount=type=bind,from=infiniflow/ragflow_deps:latest,source=/,target=/deps
         mkdir -p /etc/uv && \
         echo 'python-install-mirror = "https://registry.npmmirror.com/-/binary/python-build-standalone/"' > /etc/uv/uv.toml && \
         echo '[[index]]' >> /etc/uv/uv.toml && \
-        echo 'url = "https://pypi.tuna.tsinghua.edu.cn/simple"' >> /etc/uv/uv.toml && \
+        echo 'url = "https://mirrors.aliyun.com/pypi/simple"' >> /etc/uv/uv.toml && \
         echo 'default = true' >> /etc/uv/uv.toml; \
     fi; \
     arch="$(uname -m)"; \
@@ -167,9 +167,9 @@ COPY pyproject.toml uv.lock ./
 # uv records index url into uv.lock but doesn't failover among multiple indexes
 RUN --mount=type=cache,id=ragflow_uv,target=/root/.cache/uv,sharing=locked \
     if [ "$NEED_MIRROR" == "1" ]; then \
-        sed -i 's|pypi.org|pypi.tuna.tsinghua.edu.cn|g' uv.lock; \
+        sed -i 's|pypi.org|mirrors.aliyun.com/pypi|g' uv.lock; \
     else \
-        sed -i 's|pypi.tuna.tsinghua.edu.cn|pypi.org|g' uv.lock; \
+        sed -i 's|mirrors.aliyun.com/pypi|pypi.org|g' uv.lock; \
     fi; \
     uv sync --python 3.12 --frozen && \
     # Ensure pip is available in the venv for runtime package installation (fixes #12651)