internal/pkg: rename archive checksum helpers

These names are more consistent with other helper names, so rename them while the API is still internal.

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

internal/pkg/pkg.go

@@ -1007,7 +1007,7 @@ func (c *Cache) Scrub(checks int) error {
 
 				pathname := dir.Append(ent.Name())
 				if ent.IsDir() {
-					if err := HashDir(got, pathname); err != nil {
+					if err := SumDir(got, pathname); err != nil {
 						addErr(pathname, err)
 						return true
 					}
@@ -2132,7 +2132,7 @@ func (c *Cache) cure(a Artifact, curesExempt bool) (
 	}
 
 	var gotChecksum Checksum
-	if err = HashFS(
+	if err = SumFS(
 		&gotChecksum,
 		dotOverrideFS{os.DirFS(t.work.String()).(dirFS)},
 		".",