chore: add a custom rustfmt configuration

rustfmt.toml

@@ -0,0 +1,11 @@
+comment_width = 80
+group_imports = "StdExternalCrate"
+imports_granularity = "Module"
+max_width = 80
+newline_style = "Unix"
+normalize_comments = true
+normalize_doc_attributes = true
+reorder_impl_items = true
+tab_spaces = 2
+version = "Two"
+wrap_comments = true