internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/zstd.go

@@ -7,10 +7,11 @@ func (t Toolchain) newZstd() (pkg.Artifact, string) {
 		version  = "1.5.7"
 		checksum = "4XhfR7DwVkwo1R-TmYDAJOcx9YXv9WSFhcFUe3hWEAMmdMLPhFaznCqYIA19_xxV"
 	)
-	return t.NewPackage("zstd", version, pkg.NewHTTPGetTar(
-		nil, "https://github.com/facebook/zstd/releases/download/"+
-			"v"+version+"/zstd-"+version+".tar.gz",
-		mustDecode(checksum),
+	return t.NewPackage("zstd", version, newFromGitHubRelease(
+		"facebook/zstd",
+		"v"+version,
+		"zstd-"+version+".tar.gz",
+		checksum,
 		pkg.TarGzip,
 	), nil, &CMakeHelper{
 		Append: []string{"build", "cmake"},