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/pkg_test.go

@@ -218,7 +218,7 @@ func TestIdent(t *testing.T) {
 			},
 			nil,
 		}, unique.Make[pkg.ID](pkg.MustDecode(
-			"HnySzeLQvSBZuTUcvfmLEX_OmH4yJWWH788NxuLuv7kVn8_uPM6Ks4rqFWM2NZJY",
+			"v86qCz5fDqUsjA3KY_4LIrEh3aQnp04plNiWJ5_ap06McHSSBlROyKIFEwx3c0O7",
 		))},
 	}
 
@@ -531,7 +531,7 @@ func TestCache(t *testing.T) {
 					kind:   pkg.KindExec,
 					params: []byte("artifact overridden to be incomplete"),
 				}}, nil, pkg.Checksum{}, pkg.InvalidArtifactError(pkg.MustDecode(
-					"da4kLKa94g1wN2M0qcKflqgf2-Y2UL36iehhczqsIIW8G0LGvM7S8jjtnBc0ftB0",
+					"0z3fA0YngFaRRCQRrxKburhpAGz3gkYIZ346X_tAwOr_ldelYg1nTifI3-WX8hQD",
 				))},
 
 				{"error passthrough", newStubFile(