feat(camera): Add camera signaling models, ICE parsing utilities, and payload serialization

[Lash-L]

Summary

Implements PR 2 of the decoupled Roborock vacuum live camera streaming series (following #980, #764, #738).

This PR introduces pure Python data structures, RFC-compliant ICE candidate parsing/formatting utilities, password hashing, and WebRTC signaling serializers for Roborock camera live streaming. It adds zero external runtime dependencies (aiortc is deferred to PR 4).

Scope & Components

1. Camera Signaling Models:

   • CameraQuality (StrEnum: HD, SD).
   • CameraTurnServer dataclass (urls, username, credential with repr=False for security; includes from_dict helper validating TURN/STUN schemes).
   • CameraIceCandidate dataclass (encapsulates foundation, component, protocol, priority, ip, port, candidate_type, related_address, related_port, tcp_type, sdp_mid, sdp_mline_index, and arbitrary SDP extensions).

2. RFC-Compliant ICE Candidate Parser & Formatter:

   • parse_ice_candidate: RFC 5245 / 8839 / 8445 compliant parser for SDP candidate attribute lines (candidate:...).
     • Supports IPv4, IPv6, and browser mDNS (.local) addresses.
     • Supports RFC 6544 TCP types (active, passive, so).
     • Validates component ranges (1 <= component <= 256), priority bounds (1 <= priority <= 2^31 - 1), and foundation syntax.
     • Preserves unrecognized SDP extensions (ufrag, generation, network-id).
   • Formatter methods: CameraIceCandidate.to_sdp() and to_signaling_dict().

3. Security & Password Hashing:

   • hash_camera_password: Derives the lowercase hexadecimal MD5 digest of numeric camera PIN/pattern digits with strict ASCII validation and FIPS-compliant usedforsecurity=False.

4. WebRTC Payload Serialization:

   • encode_sdp_offer & decode_sdp_answer: Compact base64-encoded UTF-8 JSON packaging for send_sdp_to_robot / get_device_sdp, handling "retry" pending states while preserving SDP CRLF line integrity.
   • encode_ice_candidate & decode_ice_candidates: Base64-encoded UTF-8 JSON packaging for send_ice_to_robot / get_device_ice, with schema validation and optional ignore_invalid resilience for remote candidate streams.

5. Re-exports & Packaging:

   • Exposed under roborock.camera_signaling, roborock.data.camera, and roborock.data.

Validation

• Unit tests: 37 tests covering happy paths, RFC compliance, boundary checks, edge cases, malformed payloads, and re-exports (uv run pytest tests/test_camera_signaling.py).
• Code Quality: Passes uv run ruff check and uv run ruff format --check.
• Typing: Passes uv run mypy.
• Review: Refined through automated review iterations (Codex sol 6.1 and Claude opus 5.5).