internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/python.go

@@ -13,10 +13,10 @@ func (t Toolchain) newPython() (pkg.Artifact, string) {
 		version  = "3.14.4"
 		checksum = "X0VRAAGOlCVldh4J9tRAE-YrJtDvqfQTJaqxKPXNX6YTPlwpR9GwA5WRIZDO-63s"
 	)
-	return t.NewPackage("python", version, pkg.NewHTTPGetTar(
-		nil, "https://www.python.org/ftp/python/"+version+
+	return t.NewPackage("python", version, newTar(
+		"https://www.python.org/ftp/python/"+version+
 			"/Python-"+version+".tgz",
-		mustDecode(checksum),
+		checksum,
 		pkg.TarGzip,
 	), &PackageAttr{
 		// test_synopsis_sourceless assumes this is writable and checks __pycache__
@@ -142,11 +142,9 @@ pip3 install \
 	--prefix=/system \
 	--root=/work \
 	/usr/src/setuptools
-`, pkg.Path(AbsUsrSrc.Append("setuptools"), true, pkg.NewHTTPGetTar(
-		nil, "https://github.com/pypa/setuptools/archive/refs/tags/"+
-			"v"+version+".tar.gz",
-		mustDecode(checksum),
-		pkg.TarGzip,
+`, pkg.Path(AbsUsrSrc.Append("setuptools"), true, newFromGitHub(
+		"pypa/setuptools",
+		"v"+version, checksum,
 	))), version
 }
 func init() {