Moves CAPI client initialization to a deferred function in ListOptions, simplifying command setup and improving testability. Updates tests to use the new client initialization pattern and adds more comprehensive test cases for session listing.
Introduces a new 'list' subcommand under agent-task for listing agent tasks. Implements a Copilot API client for fetching agent sessions and hydrating them with pull request data. Updates PullRequest and PRRepository types to support new fields. Adds dependencies for msgpack and tagparser.
Co-Authored-By: Babak K. Shandiz <babakks@github.com>