feat(wpcarro/emacs): Package math.el

Another Elisp library that I wrote during my manic experience of switching to
EXWM.

Change-Id: I652f5c7228332a7f5822bd408a0c0be8f7bc4b4f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6018
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

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

@@ -0,0 +1,30 @@
+{ pkgs, depot, ... }:
+
+let
+  math = pkgs.callPackage
+    ({ emacsPackages }:
+      emacsPackages.trivialBuild {
+        pname = "math";
+        version = "1.0.0";
+        src = ./math.el;
+        packageRequires =
+          (with emacsPackages; [
+            dash
+          ]) ++
+          (with depot.users.wpcarro.emacs.pkgs; [
+            maybe
+          ]);
+      })
+    { };
+
+  emacs = (pkgs.emacsPackagesFor pkgs.emacs28).emacsWithPackages (epkgs: [
+    math
+  ]);
+in
+math.overrideAttrs (_old: {
+  doCheck = true;
+  checkPhase = ''
+    ${emacs}/bin/emacs -batch \
+      -l ert -l ${./tests.el} -f ert-run-tests-batch-and-exit
+  '';
+})