ByIDs implements sort.Interface for []keys.Signer based on the sorted public IDs() for each Signer. This facilitates deterministic order of signatures, which prevents tests that use fixtures from being flaky.
type ByIDs []keys.Signer
func (b ByIDs) Len() int
func (b ByIDs) Less(i, j int) bool
func (b ByIDs) Swap(i, j int)