feat(task): add completion plugin (#13313)

plugins/task/README.md

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+# Buf plugin
+
+This plugin adds completion for [Task CLI](https://taskfile.dev/), a fast, cross-platform build tool inspired by Make, designed for modern workflows.
+
+To use it, add `task` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... task)
+```

plugins/task/task.plugin.zsh

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+# Autocompletion for the task CLI (task).
+if (( !$+commands[task] )); then
+  return
+fi
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `task`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_task" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _task
+  _comps[task]=_task
+fi
+
+# Generate and load task completion
+task --completion zsh >! "$ZSH_CACHE_DIR/completions/_task" &|