[orchestra] extract graph logic and enhance with cycle detection + coloring

node/orchestra/proc-macro/Cargo.toml

@@ -20,6 +20,7 @@ proc-macro2 = "1.0.37"
 proc-macro-crate = "1.1.3"
 expander = { version = "0.0.6", default-features = false }
 petgraph = "0.6.0"
+itertools = { version = "0.10.3", optional = true }
 
 [dev-dependencies]
 assert_matches = "1.5"
@@ -28,10 +29,10 @@ thiserror = "1"
 tracing = "0.1"
 
 [features]
-default = []
+default = ["graph"]
 # write the expanded version to a `orchestra-expansion.[a-f0-9]{10}.rs`
 # in the `OUT_DIR` as defined by `cargo` for the `expander` crate.
 expand = []
 # Create directional message consuming / outgoing graph.
 # Generates: `${OUT_DIR}/${orchestra|lowercase}-subsystem-messaging.dot`
-graph = []
+graph = ["itertools"]