feat: tart macOS vm's as job container (#33)

adds the tart:// protocol to platform mapping

e.g. `-P macos-14=tart://ghcr.io/cirruslabs/macos-sonoma-base:latest` if you have a mac.

`add-path` is probably broken

pkg/tart/config_darwin.go

@@ -0,0 +1,9 @@
+package tart
+
+type Config struct {
+	SSHUsername string
+	SSHPassword string
+	Softnet     bool
+	Headless    bool
+	AlwaysPull  bool
+}