Implement checkpoint call for staking

[Adamantios]

No description provided.

[DavidMinarsch]

This means all services, even non-staking ones need to transition here...

[Adamantios]

Correct. Conceptually, it would not make much sense to add a check to any of the existing rounds on whether we should transition here or not. Therefore, CallCheckpointRound is always entered and immediately exits if the service is not staked.

[DavidMinarsch]

Why do we need this?

[Adamantios]

In order to perform the contract calls in a serialized manner, and only continue to the next step if the current call succeeded. Otherwise, the behaviour sleeps and retries the same call.

[DavidMinarsch]

This doesn't make sense for non-staking services.

I would have preferred non-staking services never reach this FSM. But given this design, you need at least some sort of boolean to track if this service even needs to do anything here.

[DavidMinarsch]

I mean now that it is implemented this way, it will work..

[Adamantios]

It does have a boolean in the synced data and checks on-chain only during the first period:

trader/packages/valory/skills/staking_abci/behaviours.py

Lines 230 to 232 in 908bc84

	if self.synchronized_data.period_count != 0:
	self.is_service_staked = self.synchronized_data.is_service_staked
	return True

If not staked, it does nothing:

trader/packages/valory/skills/staking_abci/behaviours.py

Lines 298 to 310 in 908bc84

	checkpoint_tx_hex = None
	if self.is_service_staked:
	yield from self.wait_for_condition_with_sleep(self._get_next_checkpoint)
	if self.is_checkpoint_reached:
	checkpoint_tx_hex = yield from self._prepare_safe_tx()
	tx_submitter = self.matching_round.auto_round_id()
	payload = CallCheckpointPayload(
	self.context.agent_address,
	tx_submitter,
	checkpoint_tx_hex,
	self.is_service_staked,
	)

As mentioned above, it would not make much sense conceptually to check whether the service is staked in any of the other abcis.
Moreover, this implementation makes this component as much independent as possible, so that future services can easily make use of it.