fix: use UV_CACHE_DIR for dependency caching

[k82cn]

Summary

This PR fixes the dependency caching mechanism for flamepy so that cached packages are available at runtime.

Changes

• flmadm: Use uv pip install --target instead of non-existent uv pip download to populate the cache
• flmadm: Set UV_CACHE_DIR to ${FLAME_HOME}/data/cache/uv during installation
• common: Add UV_CACHE_DIR environment variable to the flmrun application configuration
• executor_manager: Expand environment variables (like ${FLAME_HOME}) in application environment settings

Why this is needed

PR #355 introduced flamepy wheel building during installation, but the dependency caching used uv pip download which doesn't exist. Additionally, the cache was stored in the default location (~/.cache/uv) which may not be available at runtime in Docker containers.

This PR ensures:

1. Dependencies are properly cached during flmadm install
2. The cache is stored in a known location (${FLAME_HOME}/data/cache/uv)
3. The flmrun application uses the same cache location at runtime
4. Environment variables in application configs are properly expanded

[gemini-code-assist]

Summary of Changes

Hello @k82cn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses critical issues with flamepy's dependency caching, ensuring that Python package dependencies are correctly cached during installation and made available to applications at runtime. It rectifies the use of an incorrect uv command for caching and standardizes the cache location, while also enabling proper expansion of environment variables within application configurations.

Highlights

• Dependency Caching Mechanism: The dependency caching for flamepy has been fixed to ensure cached packages are available at runtime.
• flmadm Installation: Changed flmadm to use uv pip install --target instead of the non-existent uv pip download command to populate the cache.
• UV Cache Directory Configuration: The UV_CACHE_DIR environment variable is now explicitly set to ${FLAME_HOME}/data/cache/uv during installation and for the flmrun application.
• Environment Variable Expansion: The executor_manager now expands environment variables (like ${FLAME_HOME}) within application environment settings.

Changelog

• common/src/lib.rs
  • Introduced uv_cache_dir variable to define the UV cache path.
  • Configured the flmrun application to use UV_CACHE_DIR in its environment.
• executor_manager/src/shims/host_shim.rs
  • Implemented expansion of environment variables within application environment settings using Self::expand_env_vars.
• flmadm/src/managers/installation.rs
  • Replaced uv pip download with uv pip install --target for dependency caching.
  • Set the UV_CACHE_DIR environment variable for the uv pip install command to a specific path.
  • Created and cleaned up a temporary cache_target directory for the installation process.
  • Updated console output messages to reflect caching instead of downloading.

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[gemini-code-assist]

Code Review

This pull request correctly fixes the dependency caching mechanism by using uv pip install --target to populate a dedicated cache directory and configuring the runtime to use it. The changes are logical and well-implemented. I've identified one minor improvement opportunity in error handling to make the installation process more robust by failing explicitly if a temporary directory cannot be created.