internal/rosa: helpers for common url formats

This cleans up call site of NewPackage.

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

internal/rosa/kmod.go

@@ -7,10 +7,10 @@ func (t Toolchain) newKmod() (pkg.Artifact, string) {
 		version  = "34.2"
 		checksum = "0K7POeTKxMhExsaTsnKAC6LUNsRSfe6sSZxWONPbOu-GI_pXOw3toU_BIoqfBhJV"
 	)
-	return t.NewPackage("kmod", version, pkg.NewHTTPGetTar(
-		nil, "https://www.kernel.org/pub/linux/utils/kernel/"+
+	return t.NewPackage("kmod", version, newTar(
+		"https://www.kernel.org/pub/linux/utils/kernel/"+
 			"kmod/kmod-"+version+".tar.gz",
-		mustDecode(checksum),
+		checksum,
 		pkg.TarGzip,
 	), nil, &MesonHelper{
 		Setup: []KV{