New `egui_inspection` crate ships:
- `protocol` (default): wire types + length-prefixed msgpack framing for the
inspector ↔ egui-peer connection. Transport-neutral (stdio / unix socket / TCP).
- `plugin`: `InspectionPlugin`, an `egui::Plugin` that dials a unix socket from
`EGUI_INSPECTION_SOCKET`, streams frames + accesskit tree updates, and applies
inbound `InspectorCommand`s back into the running `egui::Context`.
eframe gains an `inspection` feature that auto-attaches the plugin during native
startup (glow + wgpu integrations) when the env var is set. Connection failures
log via `log::warn!` and do not abort startup.
Lives in its own crate (rather than `egui_kittest`) so eframe can pull the
protocol in without picking up the test harness, and so external tools can
depend on it directly.
