feat(nix): nix and back again

I tried Nix, but it had too many downsides so I removed it.

1. Didn't like that all files are immutable and simple config changes
need a complete rebuild.
2. Setting up a new Mac didn't work as smoothly as promised. Not worth
the effort.
3. It sucked a lot to always have to type in the password twice on each
darwin-rebuild
4. It solves problems I never had.

.config/nvim/lua/plugins/flash.lua

@@ -0,0 +1,33 @@
+-- flash.nvim
+-- https://github.com/folke/flash.nvim
+return {
+  "folke/flash.nvim",
+  event = "VeryLazy",
+  opts = {},
+  keys = {
+    {
+      "s",
+      mode = { "n", "x", "o" },
+      function()
+        require("flash").jump()
+      end,
+      desc = "Flash",
+    },
+    {
+      "S",
+      mode = { "n", "o", "x" },
+      function()
+        require("flash").treesitter()
+      end,
+      desc = "Flash Treesitter",
+    },
+    {
+      "r",
+      mode = "o",
+      function()
+        require("flash").remote()
+      end,
+      desc = "Remote Flash",
+    },
+  },
+}