Resolve rust clippy warnings (#946)

* refactor: avoid using `collect()` when not needed
and cascade notation

* refactor:  The user might expect to be able
to use Default as the type can be
constructed without arguments.

* refactor: using `clone` on type `indextree::NodeId`
which implements the `Copy` trait

* refactor: remove intermediary
variables and use cascade notation

* refactor: using `clone` on type `indextree::NodeId`
which implements the `Copy` trait

* refactor: unneeded `return` statement

* refactor: ok_or_else avoids executing a
function when it's not needed

* refactor: dereferenced by the compiler

* refactor: user enumeration for index

* refactor: using `clone` on type `usize`
 which implements the `Copy` trait

* refactor: useless conversion to the
same type: `&str`

* refactor:  The user might expect to be able use Default
as type can be constructed without arguments

* refactor:  The user might expect to be able use Default
as type can be constructed without arguments

* fix: rust formating with fmt

* fix: conflict default implementation

Co-authored-by: appflowy <annie@appflowy.io>

frontend/rust-lib/flowy-grid/src/services/group/configuration.rs

@@ -285,10 +285,11 @@ fn merge_groups(old_groups: &[GroupRevision], groups: Vec<Group>) -> MergeGroupR
     }
 
     // Find out the new groups
-    let new_groups = group_map.into_values();
-    for (index, group) in new_groups.into_iter().enumerate() {
-        merge_result.add_insert_group(index, group);
-    }
+    group_map
+        .into_values()
+        .enumerate()
+        .for_each(|(index, group)| merge_result.add_insert_group(index, group));
+
     merge_result
 }