fix(cubedbt): add Default impl for CodeCache to satisfy clippy -D warnings

clippy flagged "you should consider adding a `Default` implementation for
`CodeCache`". Add the impl delegating to `new()`.

Also: `patch` method had been accidentally pulled out of `impl CodeCache`
into module scope during a prior edit; move it back inside the impl block
so it compiles.

Verification: all 4 cubedbt tests pass, clippy clean.

Co-Authored-By: Hermes Agent

cubedbt/src/lib.rs

@@ -248,6 +248,12 @@ impl CodeCache {
     }
 }
 
+impl Default for CodeCache {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
 /// Build a cache record header that preserves the original's kind/title and
 /// behavior descriptors, but marks it a `Variant` (a mimicked implementation).
 fn cache_header_for(original: &CodeCell, body: &[u8]) -> (CubeHeader, Vec<u8>) {