bootstrap: add module docs for core:metadata

src/bootstrap/src/core/metadata.rs

@@ -1,3 +1,10 @@
+//! This module interacts with Cargo metadata to collect and store information about
+//! the packages in the Rust workspace.
+//!
+//! It runs `cargo metadata` to gather details about each package, including its name,
+//! source, dependencies, targets, and available features. The collected metadata is then
+//! used to update the `Build` structure, ensuring proper dependency resolution and
+//! compilation flow.
 use std::collections::BTreeMap;
 use std::path::PathBuf;