chore(rustfmt): standardize rustfmt config (#24135)

Standardizes the Rustfmt config filename and options, then applies cargo
fmt.

.rustfmt.toml

@@ -7,6 +7,8 @@ use_small_heuristics = "Max"
 use_field_init_shorthand = true
 
 reorder_modules = true
+merge_derives = true
+remove_nested_parens = true
 
 # All unstable features that we wish for
 # unstable_features = true