feat: DreamView (Razer) sub-protocol for per-segment LED control over LAN

[ir1141]

The crate currently has no support for DreamView - the binary sub-protocol that enables real-time per-segment LED color control over LAN UDP (sent as base64-encoded payloads inside "razer" JSON commands on port 4003).

This is useful for ambient lighting, music visualization, and any use case that needs to address individual LED segments at high frame rates (~30 fps).

Proposed changes:

• New src/dreamview.rs module with packet codec (activate, deactivate, segment colors, checksums, base64/JSON wrapping)
• DreamViewBackend async trait (separate from GoveeBackend since DreamView is LAN-only)
• DreamViewBackend implementation for LocalBackend with per-device session tracking
• DreamviewSession RAII guard with #[must_use], async close(self), and guarded Drop fallback
• DreamViewSegmentLimit and DreamViewSessionConflict error variants
• Unit tests for all packet building and protocol invariants

[ir1141]

Implementation is ready at ir1141/govee-1:dev/i131-dreamview (4 commits, all tests passing). Happy to open a PR once I have collaborator access, or feel free to pull the branch directly.

[ir1141]

I wrote an interactive CLI tester for exercising Govee lights on the local network. It's at examples/tester.rs in my fork. It covers basic controls (power, color, brightness, color temp, scenes) as well as DreamView segment colors with several built-in demo effects (rainbow, pulse, fire, storm, rave, wave, police).

Note: I only have LED strips, so I can't say how any of this behaves on a single LED light (e.g. a bulb). The DreamView segment addressing in particular may work quite differently on non-strip devices.