feat(performance): Add explain-pause-mode

This might come in handy with debugging what causing slowdowns in emacs.

core/siren-core-modules.el

@@ -43,6 +43,7 @@
 (require 'siren-flycheck)
 
 ;; Misc.
+(require 'siren-explain-pause)
 (require 'siren-grip)
 (require 'siren-restart-emacs)
 (require 'siren-zone)