feat(pack): add nushell language pack (#1601)

* feat: add nushell language pack

* chore: remove unused handlers section and specify nushell in readme

Author: cfbender

lua/astrocommunity/pack/nushell/README.md

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+# Nushell Language pack
+Requires:
+
+- A local [nufmt](https://github.com/nushell/nufmt) installation
+- A local [nushell](https://www.nushell.sh/) installation for the LSP
+
+This plugin pack does the following:
+
+- Adds `nushell` treesitter parsers
+- Adds [`nushell`](https://github.com/nushell/nushell/tree/main/crates/nu-lsp) language server
+- Adds `nufmt` as the default formatter for nushell

lua/astrocommunity/pack/nushell/init.lua

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+return {
+  {
+    "nvim-treesitter/nvim-treesitter",
+    optional = true,
+    opts = function(_, opts)
+      if opts.ensure_installed ~= "all" then
+        opts.ensure_installed = require("astrocore").list_insert_unique(opts.ensure_installed, { "nu" })
+      end
+    end,
+  },
+  {
+    "AstroNvim/astrolsp",
+    optional = true,
+    ---@type AstroLSPOpts
+    opts = {
+      servers = { "nushell" },
+    },
+  },
+  {
+    "stevearc/conform.nvim",
+    optional = true,
+    opts = {
+      formatters_by_ft = {
+        nu = { "nufmt" },
+      },
+    },
+  },
+}