feat(repository): add Cargo manifest parser
Add a standalone, unit-tested module that parses Cargo.toml manifests:
workspace member/exclude globs, package name, and internal (path-based)
dependencies, including workspace-inherited (`{ workspace = true }`) deps
resolved against the workspace root.
This is the first building block toward treating Rust crates as Turborepo
packages. It is intentionally decoupled from the existing PackageManager /
PackageJson machinery; discovery and package-graph wiring follow in later
iterations.
https://claude.ai/code/session_014BEtoj4wxFHGipkRgJUBxi
