internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/curl.go

@@ -7,9 +7,9 @@ func (t Toolchain) newCurl() (pkg.Artifact, string) {
 		version  = "8.19.0"
 		checksum = "YHuVLVVp8q_Y7-JWpID5ReNjq2Zk6t7ArHB6ngQXilp_R5l3cubdxu3UKo-xDByv"
 	)
-	return t.NewPackage("curl", version, pkg.NewHTTPGetTar(
-		nil, "https://curl.se/download/curl-"+version+".tar.bz2",
-		mustDecode(checksum),
+	return t.NewPackage("curl", version, newTar(
+		"https://curl.se/download/curl-"+version+".tar.bz2",
+		checksum,
 		pkg.TarBzip2,
 	), &PackageAttr{
 		// remove broken test