Rust: macro_rules! definitions are dropped and their invocations never resolve #4024

Summary

A macro_rules! macro is not extracted: it never becomes a node, and a name!(...) invocation of a locally-defined macro resolves to nothing.

Repro

macro_rules! my_vec {
    ($($x:expr),*) => { vec![$($x),*] };
}
fn build() -> Vec<i32> {
    my_vec!(1, 2, 3)
}

No my_vec node, no build -> my_vec edge.

Cause

The macro_definition node type has no branch in the walker, so the macro is dropped. Invocations are macro_invocation nodes (never call_expression), which walk_calls doesn't handle, so even if the definition existed there would be nothing linking to it.

Expected

Emit a node per macro_definition and resolve a bare name! invocation to it with a calls edge. A macro and a function can share a name (vec! vs vec), so macros should be tracked separately / id-qualified to avoid cross-binding. A scoped invocation (log::info!) is cross-crate and should stay unresolved (fail-closed).

Fix + regression tests ready.