feat: add read commands for plans, suites, and cases (#401)

[cosmicdreams]

Adds read-only CLI commands for fetching TestRail plans, suites, and cases as JSON:

• get_plans --project-id
• get_plan --plan-id
• get_suites --project-id
• get_cases --project-id --suite-id [--section-id]
• get_case --case-id

These commands make it possible to pull TestRail definitions into automation workflows without dropping to raw API calls.

Notes for reviewers

• Commands use the existing TestRail API endpoints and support paginated responses.
• Successful read output is clean JSON on stdout, suitable for jq and scripts.
• Auth, proxy, TLS, timeout, config, and environment handling use the existing CLI plumbing.
• Shared helper coverage was added for pagination, client option forwarding, and error handling.

Validation

• python3 -m pytest -c ./tests/pytest.ini -W ignore::pytest.PytestCollectionWarning tests
• python3 -m compileall trcli
• git diff --check

[acuanico-tr-galt]

Hi @cosmicdreams, thank you for submitting this PR. Once ready, can you point this to release/1.13.4 instead of main? We'll be reviewing the changes before we can merge. Thank you.

[acuanico-tr-galt]

This has been implemented in TRCLI v1.15.0.