Document MLC_REPO_LOCK_TIMEOUT

[anandhu-eng]

Stack: #265 ← #323 ← #325 ← #326. Merge in that order: #323 into #265's branch first, then each next PR. This PR targets #323's branch.

#265 adds the MLC_REPO_LOCK_TIMEOUT environment variable (default 1800 s). The timeout error tells users to raise it, but nothing documented it.

Changes

• mlc/repo_action.py: extends the comment next to REPO_LOCK_TIMEOUT_ENV, so the full behaviour is described where the variable is defined:
  • units (seconds, float) and the 1800 s default
  • which commands use it: pull repo and rm repo
  • fallback rules: unset or empty silently uses the default; non-numeric or ≤ 0 values also use the default, with a warning
  • when a timeout still counts as success
  • that it doesn't affect the 60 s repos.json lock
• docs/targets/repo/index.md: adds one bullet to the Pull section's notes. It says pull waits while another process holds the repo, what the default is, and how to raise it.

Comment and docs only; no code changes. Unit tests pass locally (121).

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🤖 AI PR Review Summary

This PR adds documentation and code comments about the repo lock timeout behavior for the mlc pull repo action, introducing the MLC_REPO_LOCK_TIMEOUT environment variable to control how long the process waits for a repo lock before timing out. This improves clarity on concurrency handling and timeout configuration. No design issues or risks are apparent from the diff; the changes are purely informational and do not alter functionality.