feat(wfe-rustlang): add Rust toolchain step executors

New crate providing cargo and rustup step types for WFE workflows:

Cargo steps: build, test, check, clippy, fmt, doc, publish
Rustup steps: rust-install, rustup-toolchain, rustup-component, rustup-target

Shared CargoConfig base with toolchain, package, features, release,
target, profile, extra_args, env, working_dir, and timeout support.
Toolchain override via rustup run for any cargo command.

wfe-rustlang/Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "wfe-rustlang"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+homepage.workspace = true
+description = "Rust toolchain step executors (cargo, rustup) for WFE"
+
+[dependencies]
+wfe-core = { workspace = true }
+tokio = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+async-trait = { workspace = true }
+tracing = { workspace = true }
+rustdoc-types = "0.38"
+
+[dev-dependencies]
+pretty_assertions = { workspace = true }
+tokio = { workspace = true, features = ["test-util", "process"] }
+tempfile = { workspace = true }