Trying to implement `Debug` for `IdleTimeout`

[vvvviiv]

Hello, I noticed that the Debug trait isn't implemented for the IdleTimeout struct in quinn-proto/src/config.rs. I'm trying to fix it, but I'm uncertain about the preferred style for debugging messages.

I have come up with two ways to fix it:

1. Simply use the Debug derive macro.

   #[derive(Default, Debug, Copy, Clone, Eq, Hash, Ord, PartialEq, PartialOrd)]
   pub struct IdleTimeout(VarInt);

2. Use the same style as the VarInt struct in quinn-proto/src/varint.rs.

   impl fmt::Debug for IdleTimeout {
   fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
       self.0.fmt(f)
   }
   }

Or am I missing something that blocks the implementation? Please let me know if there is anything else that needs to be done to implement this.

[Ralith]

Either would be fine; personally I lean towards the latter to reduce noise, but I don't think we need to overthink this.