fix(tailscale): make completion loading async

plugins/tailscale/tailscale.plugin.zsh

@@ -1,4 +1,13 @@
+if (( ! $+commands[tailscale] )); then
+  return
+fi
 
-if [ $commands[tailscale] ]; then
-  source <(tailscale completion zsh)
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `tailscale`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_tailscale" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _tailscale
+  _comps[tailscale]=_tailscale
 fi
+
+tailscale completion zsh >| "$ZSH_CACHE_DIR/completions/_tailscale" &|