treewide: Use nixpkgs fetchers for npins

plugins: switch from neodev to lazydev

docs/manual/configuring/overriding-plugins.md

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+# Overriding plugins {#ch-overriding-plugins}
+
+The [additional plugins section](#sec-additional-plugins) details the addition
+of new plugins to nvf under regular circumstances, i.e. while making a pull
+request to the project. You may _override_ those plugins in your config
+to change source versions, e.g., to use newer versions of plugins
+that are not yet updated in **nvf**.
+
+```nix
+vim.pluginOverrides = {
+  lazydev-nvim = pkgs.fetchFromGitHub {
+    owner = "folke";
+    repo = "lazydev.nvim";
+    rev = "";
+    hash = "";
+  };
+ # It's also possible to use a flake input
+ lazydev-nvim = inputs.lazydev-nvim;
+ # Or a local path 
+ lazydev-nvim = ./lazydev;
+ # Or a npins pin... etc
+};
+```
+
+This will override the source for the `neodev.nvim` plugin that is used in nvf
+with your own plugin.
+
+::: {.warning}
+
+While updating plugin inputs, make sure that any configuration that has been
+deprecated in newer versions is changed in the plugin's `setupOpts`. If you
+depend on a new version, requesting a version bump in the issues section is a
+more reliable option.
+
+:::