compiler/rust: allow CFG & BitSetStreamTrait to have a len() without also having an is_empty()

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38807>

src/compiler/rust/bitset.rs

@@ -292,6 +292,7 @@ impl FromIterator<usize> for BitSet {
     }
 }
 
+#[expect(clippy::len_without_is_empty)]
 pub trait BitSetStreamTrait {
     /// Get the next word
     ///

src/compiler/rust/cfg.rs

@@ -330,6 +330,7 @@ pub struct CFG<N> {
     nodes: Vec<CFGNode<N>>,
 }
 
+#[expect(clippy::len_without_is_empty)]
 impl<N> CFG<N> {
     /// Creates a new CFG from nodes and edges.
     pub fn from_blocks_edges(