refactor(snack): merge GroupIsInstalled into Grouper interface

GroupQuerier was an unnecessary indirection — GroupIsInstalled is a group
operation and belongs on Grouper. No v1 stability guarantee, so breaking
the interface is fine.

dnf/capabilities.go

@@ -15,7 +15,6 @@ var (
 	_ snack.RepoManager    = (*DNF)(nil)
 	_ snack.KeyManager     = (*DNF)(nil)
 	_ snack.Grouper        = (*DNF)(nil)
-	_ snack.GroupQuerier   = (*DNF)(nil)
 	_ snack.NameNormalizer = (*DNF)(nil)
 	_ snack.DryRunner      = (*DNF)(nil)
 )

dnf/parse_test.go

@@ -468,6 +468,5 @@ var (
 	_ snack.RepoManager    = (*DNF)(nil)
 	_ snack.KeyManager     = (*DNF)(nil)
 	_ snack.Grouper        = (*DNF)(nil)
-	_ snack.GroupQuerier   = (*DNF)(nil)
 	_ snack.NameNormalizer = (*DNF)(nil)
 )

pacman/capabilities.go

@@ -12,7 +12,6 @@ var (
 	_ snack.Cleaner        = (*Pacman)(nil)
 	_ snack.FileOwner      = (*Pacman)(nil)
 	_ snack.Grouper        = (*Pacman)(nil)
-	_ snack.GroupQuerier   = (*Pacman)(nil)
 	_ snack.DryRunner      = (*Pacman)(nil)
 )
 

snack.go

@@ -189,16 +189,12 @@ type Grouper interface {
 
 	// GroupInstall installs all packages in a group.
 	GroupInstall(ctx context.Context, group string, opts ...Option) error
-}
 
-// GroupQuerier provides an efficient check for whether a package group is
-// fully installed. This is an optional extension of [Grouper].
-// Supported by: pacman, dnf/yum.
-type GroupQuerier interface {
 	// GroupIsInstalled reports whether all packages in the group are installed.
 	GroupIsInstalled(ctx context.Context, group string) (bool, error)
 }
 
+
 // NormalizeName provides package name normalization.
 // Supported by: apt (strips :arch suffixes), rpm.
 type NameNormalizer interface {