feat(wpcarro/emacs): Package fs.el

According to SourceGraph, this is unused, but I'm checking it in for historical
purposes.

Change-Id: I24bcb1c71a9f6de527bb54057cf13d01493c45bf
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6016
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/emacs/pkgs/fs/default.nix

@@ -0,0 +1,29 @@
+{ pkgs, depot, ... }:
+
+let
+  fs = pkgs.callPackage
+    ({ emacsPackages }:
+      emacsPackages.trivialBuild {
+        pname = "fs";
+        version = "1.0.0";
+        src = ./fs.el;
+        packageRequires =
+          (with emacsPackages; [
+            dash
+            f
+            s
+          ]);
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
+    fs
+  ]);
+in
+fs.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+})