create inherent provider interface

[EclesioMeloJunior]

Description

Here is the part that connects BABE with Provisioner subsystem. Currently, Gossamer does not have a specific struct for inherents, we only define inherents at the moment of block building.

To have a better separation of responsibility we can define an interface InherentProvider and the block builder can have a set of InherentProvider.

We can define the interface in the packagelib/babe, also we can make it generic over the type of inherent it will return.

type InherentProvider interface {
    // Provide will add the data to `out`
    Provide(out *types.InherentData) T
}

type TimestampInherentProvider struct {}
// slot inherent provider might need timestamp as depedency provider
type SlotInherentProvider struct {}
// needs the overseer and state as depedencies
type ParachainsInherentProvider struct {}

• Change the BlockBuilder at lib/babe/build.go to have a set of InherentProviders and iterate over them passing a fresh *types.InherentData and them encode it.
• Changes might be needed to make timestamp and slot to conform with InherentProvider interface
• Given that we now when a slot ends (slot start + duration) set up a timeout timer to avoid going beyond the block producer time slot.

endAt := slot.start + slot.duration
remainingTime := time.NewTimer(end_at - time.Now())

go create_inherent_data()

select {
case id := <- inherentDataCh:
   // happy path, we got the inherents in time
case remainingTime.C:
   // timeout! inherents not provided in time
}

Reference

https://github.com/paritytech/polkadot-sdk/blob/c0b734336a68b6f48ac70a9b9507d8ddb9fed57e/polkadot/node/service/src/lib.rs#L1245
https://github.com/paritytech/polkadot-sdk/blob/c0b734336a68b6f48ac70a9b9507d8ddb9fed57e/substrate/client/consensus/slots/src/lib.rs#L250