Type and paginate group members

[terjekv]

Why

The Hubuum v0.0.3 group-members endpoint is cursor-paginated and returns the PrincipalMemberResponse contract, but the client exposed raw dictionaries and silently converted any non-array response to []. That hid malformed server responses and left membership pagination unavailable through the typed API.

What changed

• replace the incomplete internal Principal shape with the exported, contract-complete PrincipalMember model
• return PrincipalMember values from synchronous and asynchronous groups.members()
• add members_page(), member_pages(), and bounded all_members() helpers with sync/async parity
• route membership decoding through the shared typed page decoder so malformed responses raise DecodeError
• update unit, e2e, README, querying documentation, and the unreleased changelog

Verification

• uv sync --extra dev
• uv run ruff format --check .
• uv run ruff check . (including active PLR0913)
• uv run mypy
• uv run bandit -q -r src scripts
• uv run zizmor .
• uv run pytest --cov — 69 passed, 96.00% coverage
• uv run mkdocs build --strict
• uv build

The local Docker daemon remained unresponsive even to docker ps, so the pinned Hubuum v0.0.3 e2e workflow in CI is the live compatibility authority for this PR.

Review focus

The public return type changes from dictionaries to frozen Pydantic values. This is intentional for the typed-client contract and is documented in the changelog.