fix(editor): Improve reliability of undo history

The undo history feature of undo-tree has been very unreliable lately,
to the point it fails to load undo history for nearly every file.

It seems the undohist package is a lot more reliable.

core/siren-core-modules.el

@@ -32,6 +32,7 @@
 (require 'siren-rainbow)
 (require 'siren-smex)
 (require 'siren-undo-tree)
+(require 'siren-undohist)
 
 ;; Help
 (require 'siren-helpful)

modules/editor/siren-undo-tree.el

@@ -7,7 +7,9 @@
 ;;; Code:
 
 (use-package undo-tree
-  :demand
+  :hook
+  (after-init . global-undo-tree-mode)
+
   :bind
   ("C-x u" . undo-tree-visualize)
   ("M--" . undo-tree-undo)
@@ -22,10 +24,7 @@
   ;; autosave the undo-tree history
   (undo-tree-history-directory-alist
    `((".*" . ,(expand-file-name "undo-tree-history" siren-cache-dir))))
-  (undo-tree-auto-save-history t)
-
-  :config
-  (global-undo-tree-mode))
+  (undo-tree-auto-save-history nil))
 
 (provide 'siren-undo-tree)
 ;;; siren-undo-tree.el ends here

modules/editor/siren-undohist.el

@@ -0,0 +1,19 @@
+;;; siren-undohist.el --- jimeh's Emacs Siren: undohist configuration.
+
+;;; Commentary:
+
+;; Basic configuration for undohist.
+
+;;; Code:
+
+(use-package undohist
+  :demand
+  :custom
+  (undohist-directory (expand-file-name "undohist" siren-cache-dir))
+  (undohist-ignored-files '("COMMIT_EDITMSG"))
+
+  :config
+  (undohist-initialize))
+
+(provide 'siren-undohist)
+;;; siren-undohist.el ends here