chore: Add rustfmt configuration

pan93412 · pan93412 · commit 617bd2aa7ffc · 2022-08-30T00:25:50.000+08:00
diff --git a/rustfmt.toml b/rustfmt.toml
@@ -0,0 +1,4 @@
+unstable_features = true
+imports_granularity = "Module"
+group_imports = "StdExternalCrate"
+imports_layout = "HorizontalVertical"
