feat(emacs): Add telega.el support

Packages the telega-server binary and adds the required mode into
Emacs.

Unread message count is displayed in the modeline, which is neat.

Probably need to figure out some key bindings for this.

tools/emacs/config/init.el

@@ -171,6 +171,7 @@
 (use-package nix-util)
 (use-package nginx-mode)
 (use-package rust-mode)
+(use-package telega :config (telega-mode-line-mode 1))
 (use-package terraform-mode)
 (use-package toml-mode)
 (use-package web-mode)

tools/emacs/default.nix

@@ -11,6 +11,9 @@ let
   localPackages = pkgs.tools.emacs-pkgs;
   emacsWithPackages = (third_party.emacsPackagesNgGen third_party.emacs26).emacsWithPackages;
 
+  # $PATH for binaries that need to be available to Emacs
+  emacsBinPath = lib.makeBinPath [ third_party.telega ];
+
   identity = x: x;
   tazjinsEmacs = pkgfun: (emacsWithPackages(epkgs: pkgfun(
   # Actual ELPA packages (the enlightened!)
@@ -68,6 +71,7 @@ let
     sly
     string-edit
     swiper
+    telega
     telephone-line
     terraform-mode
     toml-mode
@@ -90,6 +94,7 @@ let
     term-switcher
   ]))));
 in lib.fix(self: l: f: third_party.writeShellScriptBin "tazjins-emacs" ''
+  export PATH="${emacsBinPath}:$PATH"
   exec ${tazjinsEmacs f}/bin/emacs \
     --debug-init \
     --no-site-file \
@@ -109,6 +114,7 @@ in lib.fix(self: l: f: third_party.writeShellScriptBin "tazjins-emacs" ''
     # Build a derivation that uses the specified local Emacs (i.e.
     # built outside of Nix) instead
     withLocalEmacs = emacsBin: third_party.writeShellScriptBin "tazjins-emacs" ''
+      export PATH="${emacsBinPath}:$PATH"
       export EMACSLOADPATH="${(tazjinsEmacs f).deps}/share/emacs/site-lisp:"
       exec ${emacsBin} \
         --debug-init \