perf: remove unnecessary clone in set_subcommand_ancestors

Replace `ancestors.to_vec()` followed by `ancestors.clone().into_iter()`
with direct `ancestors.iter().cloned()`. This eliminates two Vec allocations
per recursion level (one for the to_vec() and one for each subcommand's clone()).

The improvement:
- Before: O(n) Vec allocation for to_vec() + O(n) Vec allocation per subcommand
- After: O(n) lazy iteration with element-by-element cloning (no intermediate Vec)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jdx

lib/src/spec/mod.rs

@@ -309,14 +309,14 @@ fn extract_usage_from_comments(full: &str) -> String {
 }
 
 fn set_subcommand_ancestors(cmd: &mut SpecCommand, ancestors: &[String]) {
-    let ancestors = ancestors.to_vec();
     for subcmd in cmd.subcommands.values_mut() {
         subcmd.full_cmd = ancestors
-            .clone()
-            .into_iter()
+            .iter()
+            .cloned()
             .chain(once(subcmd.name.clone()))
             .collect();
-        set_subcommand_ancestors(subcmd, &subcmd.full_cmd.clone());
+        let child_ancestors = subcmd.full_cmd.clone();
+        set_subcommand_ancestors(subcmd, &child_ancestors);
     }
     if cmd.usage.is_empty() {
         cmd.usage = cmd.usage();