internal/rosa: pass stage alongside state

This cleans up many function signatures.

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

internal/rosa/xz.go

@@ -2,12 +2,12 @@ package rosa
 
 import "hakurei.app/internal/pkg"
 
-func (t Toolchain) newXZ(s *S) (pkg.Artifact, string) {
+func (t Toolchain) newXZ() (pkg.Artifact, string) {
 	const (
 		version  = "5.8.3"
 		checksum = "nCdayphPGdIdVoAZ2hR4vYlhDG9LeVKho_i7ealTud4Vxy5o5dWe0VwFlN7utuUL"
 	)
-	return s.NewPackage(t, "xz", version, newFromGitHubRelease(
+	return t.NewPackage("xz", version, newFromGitHubRelease(
 		"tukaani-project/xz",
 		"v"+version,
 		"xz-"+version+".tar.bz2",