test(cli, download): add 17 gap-coverage tests for Phase 7
CLI: clear-cache (existing + missing), path (ok + error), fetch happy
path, no/unknown subcommand error paths. Calls cli.main() directly
instead of subprocess to keep tests fast and capture stderr cleanly.
Download: cache hit skips HTTP, tar.gz extraction, comment/blank
checksum lines, unknown archive format, missing entry after extract,
unsupported platform. Also covers pure helpers _parse_owner_repo,
_sha256_file, and _github_token env precedence.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
chrissbaumann
ca8d815216