Separate test and example for Irisawa hexlet

Put shared code in the conditionally compiled `engine::irisawa` module.

app-proto/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 
 [features]
 default = ["console_error_panic_hook"]
+irisawa = []
 
 [dependencies]
 itertools = "0.13.0"
@@ -36,7 +37,12 @@ features = [
   'WebGlVertexArrayObject'
 ]
 
+# the self-dependency specifies features to use for tests and examples
+#
+#   https://github.com/rust-lang/cargo/issues/2911#issuecomment-1483256987
+#
 [dev-dependencies]
+dyna3 = { path = ".", default-features = false, features = ["irisawa"] }
 wasm-bindgen-test = "0.3.34"
 
 [profile.release]