Major optimization refactor, across the board

+ enable lexical-scope everywhere (lexical-binding = t): ~5-10% faster
  startup; ~5-20% general boost
+ reduce consing, function calls & garbage collection by preferring
  cl-loop & dolist over lambda closures (for mapc[ar], add-hook, and
  various cl-lib filter/map/reduce functions) -- where possible
+ prefer functions with dedicated opcodes, like assq (see byte-defop's
  in bytecomp.el for more)
+ prefer pcase & cond (faster) over cl-case
+ general refactor for code readability
+ ensure naming & style conventions are adhered to
+ appease byte-compiler by marking unused variables with underscore
+ defer minor mode activation to after-init, emacs-startup or
  window-setup hooks; a customization opportunity for users + ensures
  custom functionality won't interfere with startup.

modules/app/email/config.el

@@ -1,4 +1,4 @@
-;;; app/email/config.el
+;;; app/email/config.el -*- lexical-binding: t; -*-
 
 ;; I want to live in Emacs. Living is incomplete without email, so Emacs needs
 ;; to give me the ability to read, search, write and send my email. It does so
@@ -16,9 +16,9 @@
 
 (def-setting! :email (label letvars &optional default)
   "Registers an email address for mu4e."
-  (let* ((name (or (cdr (assq 'user-full-name letvars)) user-full-name))
-         (address (cdr (assq 'user-mail-address letvars))))
-    (dolist (var letvars letvars)
+  (let ((name (or (cdr (assq 'user-full-name letvars)) user-full-name))
+        (address (cdr (assq 'user-mail-address letvars))))
+    (dolist (var letvars)
       (let ((val (cdr var)))
         (when (and (stringp val) (string-match-p "%s" val))
           (setcdr var (format val label)))))
@@ -96,15 +96,15 @@
                          ("mime:image/*" "Messages with images" ?p)))
 
   ;; Add a column to display what email account the email belongs to.
-  (push '(:account
-          :name "Account"
-          :shortname "Account"
-          :help "Which account this email belongs to"
-          :function
-          (lambda (msg)
-            (let ((maildir (mu4e-message-field msg :maildir)))
-              (format "%s" (substring maildir 1 (string-match-p "/" maildir 1))))))
-        mu4e-header-info-custom)
+  (cl-pushnew '(:account
+                :name "Account"
+                :shortname "Account"
+                :help "Which account this email belongs to"
+                :function
+                (lambda (msg)
+                  (let ((maildir (mu4e-message-field msg :maildir)))
+                    (format "%s" (substring maildir 1 (string-match-p "/" maildir 1))))))
+              mu4e-header-info-custom)
 
   ;; In my workflow, emails won't be moved at all. Only their flags/labels are
   ;; changed. Se we redefine the trash and refile marks not to do any moving.