style(rust): Format all Rust code with rustfmt

Change-Id: Iab7e00cc26a4f9727d3ab98691ef379921a33052
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5240
Tested-by: BuildkiteCI
Reviewed-by: kanepyork <rikingcoding@gmail.com>
Reviewed-by: Profpatsch <mail@profpatsch.de>
Reviewed-by: grfn <grfn@gws.fyi>
Reviewed-by: tazjin <tazjin@tvl.su>

fun/defer_rs/examples/undefer.rs

@@ -1,10 +1,10 @@
 // Go's defer in Rust, with a little twist!
 
 struct Defer<F: Fn()> {
-    f: F
+    f: F,
 }
 
-impl <F: Fn()> Drop for Defer<F> {
+impl<F: Fn()> Drop for Defer<F> {
     fn drop(&mut self) {
         (self.f)()
     }