Essentially we may want a interface with the ability to:
	i) keep as severity window (2 * era_len) -> slash after that time has expired
	ii) slash `on_end_of_era`

Then `on_signal` becomes useless.

However, it would require a change on `Slashing::slash` which probably should return `Option<MisconductLevel>`

That would return `Some(MisconductLevel)` when a window has expired otherwise return `None`.
A `reporter` would need to call `slash` even if misconducts had occured

avoid divide by zero instead do 0 / 1

These may need to be moved later

* Fix DiscoveryBehaviour::poll.

The previous implementation regularly returned `NotReady` from `poll`
despite the inner Kademlia behaviour having events ready, thus letting
the `poll`ing be largely driven by the task wakeups from the Delay for
the next random Kademlia query, inducing major delays in consuming
the ready Kademlia events and thus slowing progress.

The discovery test now passes quickly, as expected.

* Ensure the Delay is polled right after reset.

For task wakeup.

* Some cleanup

* Add module constant metadata declaration

* Begin to integrate the constants in `decl_module`

* Fixes tests

* Fix compilation and add tests

* Remove duplicate code

* Expose constants in democracy and staking + further fixes

* Update srml/metadata/src/lib.rs

Co-Authored-By: YJ <[email protected]>

* Hide `RawEvent` metadata function

* Prevent whitespaces in types

* Fix `offchain_worker` and `constants` with instances

* Up the `impl_version`

* Fix macro

* Incrase impl_version

This macro compiles and executes the given code only when `std` feature
is enabled. This can be useful for debugging without needing to worry
that your code does not compile on `no_std`.