Add egui_inspection protocol and plugin (#8234)

Introduces live inspection for running egui apps over a small TCP
request/response protocol, plus the `egui::Plugin` that serves it.

This is the minimal surface to get the egui mcp in, we may want to
extend this in the future to add support for the inspection gui.

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/egui_inspection/Cargo.toml

@@ -0,0 +1,42 @@
+[package]
+name = "egui_inspection"
+version.workspace = true
+authors = ["Lucas Meurer <hi@lucasmerlin.me>", "Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+description = "Protocol and egui::Plugin for inspection of egui apps"
+edition.workspace = true
+rust-version.workspace = true
+homepage = "https://github.com/emilk/egui"
+license.workspace = true
+readme = "./README.md"
+repository = "https://github.com/emilk/egui"
+categories = ["gui", "development-tools::testing", "accessibility"]
+keywords = ["gui", "egui", "inspector", "accesskit", "mcp"]
+include = ["../../LICENSE-APACHE", "../../LICENSE-MIT", "**/*.rs", "Cargo.toml"]
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--generate-link-to-definition"]
+
+[features]
+default = []
+
+## Screenshot PNG encoding — the `EncodedPng::from_color_image` / `from_rgba` constructors.
+png = ["dep:image", "image/png"]
+
+## `InspectionPlugin` — an `egui::Plugin` that serves the request/response inspection
+## protocol over TCP. Apps usually enable inspection by setting the `EGUI_INSPECTION` env var
+## (handled by eframe's `inspection` feature).
+plugin = ["png", "dep:log"]
+
+[dependencies]
+egui = { workspace = true, features = ["serde"] }
+serde.workspace = true
+serde_bytes = "0.11.17"
+rmp-serde.workspace = true
+
+image = { workspace = true, optional = true }
+log = { workspace = true, optional = true }
+document-features = { workspace = true, optional = true }
+
+[lints]
+workspace = true