cargo-rail: added petgraph && build WorkspaceGraph; implemented the algos needed and wired it up. Full '--git' integration.

Author: loadingalias

Cargo.lock

@@ -23,6 +23,9 @@ anstyle = "1.0.13"
 # Workspace introspection
 cargo_metadata = "0.23.1"
 
+# Graph analysis
+petgraph = "0.8.3"
+
 # Lossless TOML editing (preserves formatting)
 toml_edit = { version = "0.23.7", features = ["serde"] }