Add check waiter

[amrit110]

This pull request refactors the workflow for waiting on GitHub PR checks before auto-merging, replacing a custom Bash loop with a dedicated Python CLI command for improved maintainability and testability. The main change is the introduction of a new wait-checks CLI command, which encapsulates the logic for monitoring PR check status and provides clear exit codes for downstream automation. Supporting modules and tests have been added to enable this functionality.

Workflow and CLI integration:

• The Bash code in .github/workflows/fix-remote-pr.yml that waits for PR checks is replaced by a call to the new Python CLI command aieng-bot wait-checks, which handles check monitoring and outputs appropriate status messages based on exit codes.

New CLI command and supporting modules:

• Added the wait-checks command to the CLI (src/aieng_bot/_cli/commands/wait_checks.py), which waits for PR checks to complete, provides clear exit codes, and logs status messages for success, failure, timeout, or missing checks.
• Registered the new CLI command in the main CLI entrypoint (src/aieng_bot/_cli/main.py). [1] [2]

Core check waiter implementation:

• Implemented the CheckWaiter class and related types (CheckStatus, WaitResult) in src/aieng_bot/check_waiter/waiter.py, encapsulating the logic for querying PR check status via the GitHub CLI, analyzing results, and handling timeouts and error cases.
• Added an __init__.py to the check_waiter module to expose the new types for import.

Testing:

• Added a test module stub for the check waiter functionality (tests/check_waiter/__init__.py).