chore(all): return concrete types, accept interfaces

- Remove exported interfaces unused locally
- Define interfaces to accept arguments
- Return concrete types, not interfaces

internal/loopstate/state.go

@@ -6,15 +6,6 @@ import (
 	"github.com/qdm12/gluetun/internal/models"
 )
 
-var _ Manager = (*State)(nil)
-
-type Manager interface {
-	Locker
-	Getter
-	Setter
-	Applier
-}
-
 func New(status models.LoopStatus,
 	start chan<- struct{}, running <-chan models.LoopStatus,
 	stop chan<- struct{}, stopped <-chan struct{}) *State {