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/ui/siren-display-time.el

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

modules/ui/siren-pixel-scroll.el

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

modules/ui/siren-solaire-mode.el

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

modules/ui/siren-transparency.el

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

modules/ui/siren-ui.el

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