Add missing Variant() method to ed25519.Parameters

#tinkApiChange

PiperOrigin-RevId: 672897691
Change-Id: Iba5ac1802c6a38b8e4416c2a7a97d5e849c0500e

signature/ed25519/key.go

@@ -76,6 +76,9 @@ func NewParameters(variant Variant) (Parameters, error) {
 	return Parameters{variant: variant}, nil
 }
 
+// Variant returns the prefix variant of the parameters.
+func (p *Parameters) Variant() Variant { return p.variant }
+
 // HasIDRequirement returns true if the key has an ID requirement.
 func (p *Parameters) HasIDRequirement() bool { return p.variant != VariantNoPrefix }
 

signature/ed25519/key_test.go

@@ -43,10 +43,13 @@ func TestNewParameters(t *testing.T) {
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			_, err := ed25519.NewParameters(tc.variant)
+			params, err := ed25519.NewParameters(tc.variant)
 			if err != nil {
 				t.Errorf("ed25519.NewParameters(%v) err = %v, want nil", tc.variant, err)
 			}
+			if got := params.Variant(); got != tc.variant {
+				t.Errorf("params.Variant() = %v, want %v", got, tc.variant)
+			}
 		})
 	}
 	t.Run("unknown", func(t *testing.T) {