init: Use multithreaded xz decompression (-T0)

On my AMD Ryzen R7 2700X, unxz of a ~260GiB unstable .img.xz takes 30s.
In comparison, unxz -T0 of the same ~260GiB unstable .img.xz takes 4s.

According to the xz release notes, multithreaded compression has been
supported since xz version 5.2.0, which was released in 2014.

xz 5.2.2 was added to the Solus repos in October 2016, so all Solus
installs since then would have supported multi-threaded decompression,
making the addition of the -T0 flag in solbuild guaranteed to work on
existing systems.

The end result is a nicer user experience when updating solbuild images.

Signed-off-by: Rune Morling <[email protected]>

cli/init.go

@@ -115,7 +115,7 @@ func doInit(manager *builder.Manager) {
 	// Decompress the image
 	slog.Debug("Decompressing backing image", "source", bk.ImagePathXZ, "target", bk.ImagePath)
 
-	if err := commands.ExecStdoutArgsDir(builder.ImagesDir, "unxz", []string{bk.ImagePathXZ}); err != nil {
+	if err := commands.ExecStdoutArgsDir(builder.ImagesDir, "unxz", []string{"-T0", bk.ImagePathXZ}); err != nil {
 		slog.Error("Failed to decompress image", "source", bk.ImagePathXZ, "err", err)
 		panic(err)
 	}