* Add `protocols_handler::multi` module.
An implementation of `ProtocolsHandler` that contains multiple other
`ProtocolsHandler`s indexed by some key type.
* Randomise start position of handler polling.
* Address some review concerns.
* Add `IntoMultiHandler`.
* Check protocol names for uniqueness.
* Changes due to review.
- No more `Debug` bound for the key type and more generic log messages.
- Additional comments.
- Imports instead of fully-qualified use.
- Renamed `DuplicateProtoname` to `DuplicateProtonameError`.
* Replace `HashMap` with `Vec` in `Upgrades`.
* Review suggestion.
Co-authored-by: Roman Borschel <romanb@users.noreply.github.com>
Co-authored-by: Pierre Krieger <pierre.krieger1708@gmail.com>
