[misc] fix: add missing __init__.py files to package directories

[guillemgt]

What does this PR do?

Adds missing __init__.py files to 11 package directories that contained Python modules but were not properly configured as packages. This ensures these directories are recognized as importable Python packages.

Affected directories:

• Several directories in experimental/ (fully_async_policy, one_step_off_policy, vla/*, reward_loop/router, transfer_queue)
• tools/utils/mcp_clients/
• utils/sglang/
• workers/rollout/trtllm_rollout/

All files include proper Apache 2.0 license headers consistent with the project.

Checklist Before Starting

• Search for similar PRs. No similar PRs found: https://github.com/volcengine/verl/pulls?q=is%3Apr+init
• Format the PR title as [{modules}] {type}: {description}

Test

Confirmed that affected modules can be imported after the change.
No functional changes - only adds empty files with license headers. Existing tests should continue to pass.

Checklist Before Submitting

• Read the Contribute Guide
• Applied pre-commit checks (all relevant checks passed)
• Documentation not needed (no user-facing changes)
• No tests needed (structural fix only, no functional changes)

[gemini-code-assist]

Code Review

This pull request correctly adds missing __init__.py files to several directories, ensuring they are properly recognized as Python packages. This is a good structural improvement that enhances the project's packaging and import behavior. The changes are straightforward and correct, and I have no further comments.

[vermouth1992]

This is contributed by Nvidia

[guillemgt]

I see. I've updated the license to match the other files in the directory, however they also don't list Nvidia

[vermouth1992]

Is VLA contributed by Meituan?

[guillemgt]

No, sorry, fixed this now

[CLAassistant]

All committers have signed the CLA.