feat(charm): add plugin for `charm` (#10803)

plugins/charm/README.md

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+# Charm plugin
+
+This plugin adds completion for the [charm](https://github.com/charmbracelet/charm) CLI.
+
+To use it, add `charm` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... charm)
+```

plugins/charm/charm.plugin.zsh

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