Add transformers CLI installer

[Wauplin]

Disclaimer: partially AI-generated
- PR description: Claude Code
- _cli_utils.py: Claude Code
- install.sh: mainly me
- install.ps1: mainly Claude Code

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Summary

This PR adds support for installing the transformers CLI alongside the huggingface_hub CLI in the standalone installer scripts, and refactors the CLI update checker to support multiple libraries.

Changes

CLI Update Checker (_cli_utils.py, hf.py):

• check_cli_update() now accepts a required library parameter (Literal["huggingface_hub", "transformers"]) to check updates for different libraries
• Extracted _get_huggingface_hub_update_command() and _get_transformers_update_command() helper functions for cleaner code organization
• Updated hf.py to pass "huggingface_hub" to check_cli_update()

Installer Scripts (install.sh, install.ps1):

• Added --with-transformers flag (bash) / -WithTransformers parameter (PowerShell) to optionally install the transformers CLI
• If transformers is already installed in the venv, it automatically gets upgraded (even without the flag) to keep it in sync
• Uses importlib.metadata for fast package detection (avoids slow module import)
• Refactored common installation logic into shared install_package() / Install-Package functions
• Removed HF_CLI_VERSION environment variable support (always installs latest version)

Usage

# Install hf CLI only (default)
curl -LsSf https://hf.co/cli/install.sh | bash -s

# Install both hf and transformers CLIs
curl -LsSf https://hf.co/cli/install.sh | bash -s -- --with-transformers

# Install hf CLI only (default)
powershell -c "irm https://hf.co/cli/install.ps1 | iex"

# Install both hf and transformers CLIs
powershell -c "irm https://hf.co/cli/install.ps1 | iex" -WithTransformers

TODO

Once this PR is merged, let's release it and integrate check_cli_update into transformers CLI for auto-update detection.

[bot-ci-comment]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[hanouticelina]

looks good to me! thanks
approving the PR but i'm still not convinced about having a one liner installer for transformers here (since we try to be library agnostic as much as possible) but no strong opinion either (cc @LysandreJik if you have an opinion on that).

[Wauplin]

As discussed offline, we try to be library agnostic in huggingface_hub in general but for CLIs specifically I think it's fine to be a bit more opinionated.

So I'll merge this one and follow-up with transformers integration.

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Btw haven't mentioned in the PR description but the end goal is to be able to do

curl -LsSf https://hf.co/cli/install.sh | bash -s -- --with-transformers
transformers serve
transformers chat openai/gpt-oss-120b