Fix memory leak in when calling Metadata::get_value_store in Rust API

Forgot to free the `BNMetadataValueStore` object returned by core

Author: emesare

rust/src/metadata.rs

@@ -239,6 +239,8 @@ impl Metadata {
                     };
                     map.insert(key, value);
                 }
+                
+                unsafe { BNFreeMetadataValueStore(ptr) };
 
                 Ok(map)
             }