fix(core): unused map-key iteration in Capabilities::zeroize tripped the release gate

clippy::for_kv_map under -D warnings; main has been ungreen since before
the 0.8.1 publish. Folded into the 0.9.0 publish per review 011, but main
stays green from now.

Verified: cargo test (684), clippy --all-targets -D warnings, fmt --check.

src/core/types.rs

@@ -64,7 +64,7 @@ pub struct Capabilities {
 
 impl Zeroize for Capabilities {
     fn zeroize(&mut self) {
-        for (_, v) in self.entries.iter_mut() {
+        for v in self.entries.values_mut() {
             v.zeroize();
         }
         self.entries.clear();