cleanup: move default() functions to impl Default

As suggested by a newer version of Clippy.

lib/src/op_store.rs

@@ -28,15 +28,17 @@ impl Debug for WorkspaceId {
     }
 }
 
+impl Default for WorkspaceId {
+    fn default() -> Self {
+        Self("default".to_string())
+    }
+}
+
 impl WorkspaceId {
     pub fn new(value: String) -> Self {
         Self(value)
     }
 
-    pub fn default() -> Self {
-        Self("default".to_string())
-    }
-
     pub fn as_str(&self) -> &str {
         &self.0
     }

lib/src/repo.rs

@@ -315,14 +315,8 @@ pub struct BackendFactories {
     factories: HashMap<String, BackendFactory>,
 }
 
-impl BackendFactories {
-    pub fn empty() -> Self {
-        BackendFactories {
-            factories: HashMap::new(),
-        }
-    }
-
-    pub fn default() -> Self {
+impl Default for BackendFactories {
+    fn default() -> Self {
         let mut factories = BackendFactories::empty();
         factories.add_backend(
             "local",
@@ -334,6 +328,14 @@ impl BackendFactories {
         );
         factories
     }
+}
+
+impl BackendFactories {
+    pub fn empty() -> Self {
+        BackendFactories {
+            factories: HashMap::new(),
+        }
+    }
 
     pub fn add_backend(&mut self, name: &str, factory: BackendFactory) {
         self.factories.insert(name.to_string(), factory);