fix(elisp): add lexical-binding comment to all files to suppress new Emacs 31 warnings

I've set `lexical-binding` to `nil` in all Emacs Lisp files to suppress
the warnings introduced in Emacs 31 requiring all elisp files to have a
`lexical-binding` comment.

This retains the default behavior of dynamic binding when no
`lexical-binding` comment is present. With it set to `t` across the
board, various things break, and fixing those is a task for another day.

modules/projects/siren-dired-sidebar.el

@@ -1,4 +1,4 @@
-;;; siren-dired-sidebar.el --- jimeh's Emacs Siren: dired-sidebar configuration.
+;;; siren-dired-sidebar.el --- jimeh's Emacs Siren: dired-sidebar configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-ecb.el

@@ -1,4 +1,4 @@
-;;; siren-ecb.el --- jimeh's Emacs Siren: ECB configuration.
+;;; siren-ecb.el --- jimeh's Emacs Siren: ECB configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-editorconfig.el

@@ -1,4 +1,4 @@
-;;; siren-editorconfig.el --- jimeh's Emacs Siren: editorconfig configuration.
+;;; siren-editorconfig.el --- jimeh's Emacs Siren: editorconfig configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-helm-projectile.el

@@ -1,4 +1,4 @@
-;;; siren-helm-projectile.el --- jimeh's Emacs Siren: helm-projectile configuration.
+;;; siren-helm-projectile.el --- jimeh's Emacs Siren: helm-projectile configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-neotree.el

@@ -1,4 +1,4 @@
-;;; siren-neotree.el --- jimeh's Emacs Siren: neotree configuration.
+;;; siren-neotree.el --- jimeh's Emacs Siren: neotree configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-project-explorer.el

@@ -1,4 +1,4 @@
-;;; siren-project-explorer.el --- jimeh's Emacs Siren: project-explorer configuration.
+;;; siren-project-explorer.el --- jimeh's Emacs Siren: project-explorer configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-projectile.el

@@ -1,4 +1,4 @@
-;;; siren-projectile.el --- jimeh's Emacs Siren: projectile configuration.
+;;; siren-projectile.el --- jimeh's Emacs Siren: projectile configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary:
 

modules/projects/siren-treemacs.el

@@ -1,4 +1,4 @@
-;;; siren-treemacs.el --- jimeh's Emacs Siren: treemacs configuration.
+;;; siren-treemacs.el --- jimeh's Emacs Siren: treemacs configuration.  -*- lexical-binding: nil; -*-
 
 ;;; Commentary: