feat(ariadne): add graph module

src/ariadne/BUILD

@@ -3,7 +3,11 @@ load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_library")
 rust_library(
     name = "ariadne_lib",
     crate_name = "ariadne",
-    srcs = ["lib.rs"],
+    crate_root = "lib.rs",
+    srcs = [
+        "graph.rs",
+        "lib.rs",
+    ],
 )
 
 rust_binary(

src/ariadne/graph.rs

@@ -0,0 +1,4 @@
+//! In-memory graph model used by Ariadne pipeline stages.
+
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
+pub struct Graph;

src/ariadne/lib.rs

@@ -1,3 +1,5 @@
+pub mod graph;
+
 pub fn run() {
     println!("Ariadne");
 }