chore(all): return concrete types, accept interfaces

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

internal/alpine/alpine.go

@@ -5,13 +5,6 @@ import (
 	"os/user"
 )
 
-var _ Alpiner = (*Alpine)(nil)
-
-type Alpiner interface {
-	UserCreater
-	VersionGetter
-}
-
 type Alpine struct {
 	alpineReleasePath string
 	passwdPath        string

internal/alpine/users.go

@@ -12,10 +12,6 @@ var (
 	ErrUserAlreadyExists = errors.New("user already exists")
 )
 
-type UserCreater interface {
-	CreateUser(username string, uid int) (createdUsername string, err error)
-}
-
 // CreateUser creates a user in Alpine with the given UID.
 func (a *Alpine) CreateUser(username string, uid int) (createdUsername string, err error) {
 	UIDStr := strconv.Itoa(uid)

internal/alpine/version.go

@@ -7,10 +7,6 @@ import (
 	"strings"
 )
 
-type VersionGetter interface {
-	Version(ctx context.Context) (version string, err error)
-}
-
 func (a *Alpine) Version(ctx context.Context) (version string, err error) {
 	file, err := os.OpenFile(a.alpineReleasePath, os.O_RDONLY, 0)
 	if err != nil {