internal/rosa: pass stage alongside state

This cleans up many function signatures.

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

internal/rosa/flex.go

@@ -4,12 +4,12 @@ import (
 	"hakurei.app/internal/pkg"
 )
 
-func (t Toolchain) newFlex(s *S) (pkg.Artifact, string) {
+func (t Toolchain) newFlex() (pkg.Artifact, string) {
 	const (
 		version  = "2.6.4"
 		checksum = "p9POjQU7VhgOf3x5iFro8fjhy0NOanvA7CTeuWS_veSNgCixIJshTrWVkc5XLZkB"
 	)
-	return s.NewPackage(t, "flex", version, newFromGitHubRelease(
+	return t.NewPackage("flex", version, newFromGitHubRelease(
 		"westes/flex",
 		"v"+version,
 		"flex-"+version+".tar.gz",