Fix query loop in covenant evmulator

[KonradStaniec]

Currently query loop of covenant emulator always retrieve only one batch of pending delegations: https://github.com/babylonlabs-io/covenant-emulator/blob/v0.11.2/covenant/covenant.go#L480

This means if amount pending delegations is > limit in dels, err := ce.cc.QueryPendingDelegations(limit) call, covenant fails to move forward to sign next delegations.

Example:
Currently there is 1000 pending delegations in the system, covnenat already signed first 100 and it has limit set to 100 . Unless amount of pending delegation start decreasing, covenant will fail to move past first 100 delegations.

Actions:

• QueryPendingDelegations should return delegations which are not already signed and that expect covenant memver signature.