internal/pkg: encode checksum in ident

This also rearranges the ident ir to be more predictable, and avoids an obvious and somewhat easy to get into inconsistent state.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/file_test.go

@@ -17,13 +17,13 @@ func TestFile(t *testing.T) {
 			cureMany(t, c, []cureStep{
 				{"short", pkg.NewFile("null", []byte{0}), base.Append(
 					"identifier",
-					"lIx_W4M7tVOcQ8jh08EJOfXf4brRmkEEjvUa7c17vVUzlmtUxlhhrgqmc9aZhjbn",
+					"3nNZXzfgfDW2aHqmgf1VpJUYxe1GMzU7eA9Q_NnNVTDPpPOCTYKEVX-yscOiLT-e",
 				), pkg.MustDecode(
 					"vsAhtPNo4waRNOASwrQwcIPTqb3SBuJOXw2G4T1mNmVZM-wrQTRllmgXqcIIoRcX",
 				), nil},
 			})
 		}, pkg.MustDecode(
-			"hnrfmJtivNKcgtETsKnU9gP_OwPgpNY3DSUJnmxnmeOODSO-YBvEBiTgieY4AAd7",
+			"azjTvqkTjLhFzvPDM4DEHiHyLupOnRq9GCikVN6DEElR1Gxz_BDo4SA0zZzaYUGa",
 		)},
 	})
 }