feat(tvix/store/protos): add Deriver field to PathInfo

This uses the newly introduced StorePath message type to add a Deriver
field to the PathInfo message.

Support for validation is added to both the golang and rust
implementation. This includes extending unit tests.

Change-Id: Ifc3eb3263fa25b9eec260db354cd74234c40af7e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9647
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI

tvix/store/protos/pathinfo_test.go

@@ -120,4 +120,30 @@ func TestValidate(t *testing.T) {
 		_, err := pi.Validate()
 		assert.Error(t, err, "must not validate")
 	})
+
+	t.Run("happy deriver", func(t *testing.T) {
+		pi := genPathInfoSymlink()
+
+		// add the Deriver Field.
+		pi.Deriver = &storev1pb.StorePath{
+			Digest: exampleStorePathDigest,
+			Name:   "foo",
+		}
+
+		_, err := pi.Validate()
+		assert.NoError(t, err, "must validate")
+	})
+
+	t.Run("invalid deriver", func(t *testing.T) {
+		pi := genPathInfoSymlink()
+
+		// add the Deriver Field, with a broken digest
+		pi.Deriver = &storev1pb.StorePath{
+			Digest: []byte{},
+			Name:   "foo2",
+		}
+		_, err := pi.Validate()
+		assert.Error(t, err, "must not validate")
+	})
+
 }