selected-window-accent-mode with window colour blending options

I have enhanced selected-window-accent functionality with blending options to blend colourize the selected window (see below):

This means that not only will the mode-line, fringes and header be accent coloured, but also the whole selected window background colour, tinted to the alpha chosen.

The features added are as follows:

• Introduced selected-window-accent-use-blend-background and selected-window-accent-use-blend-alpha to allow blending of the accent colour with the background of the selected window a selected alpha amount.
• Introduced new toggle functions and added to transient:
  • selected-window-accent-toggle-blend-background
  • selected-window-accent-toggle-pywal
• Added function selected-window-accent-blend-colors to support blending of two colours.
• Updated selected-window-accent--set-foreground-color and selected-window-accent functions to incorporate new blending feature.
• Improved existing functions for setting and toggling accent features, ensuring consistent style and formatting.
• Cleaned up indentation and formatting inconsistencies across the file for better readability.

Example use of new selected window blending functionality:

(use-package selected-window-accent-mode
  :config (selected-window-accent-mode 1)
  :custom
  (selected-window-accent-fringe-thickness 10)
  (selected-window-accent-use-blend-background t)
  (selected-window-accent-use-blend-alpha 0.2)
  (selected-window-accent-tab-accent t)
  (selected-window-accent-custom-color "cyan4")
  (selected-window-accent-mode-style 'default))

(use-package selected-window-accent-mode
  :config (selected-window-accent-mode 1)
  :custom
  (selected-window-accent-fringe-thickness 10)
  (selected-window-accent-use-blend-background t)
  (selected-window-accent-use-blend-alpha 0.1)
  (selected-window-accent-tab-accent t)
  (selected-window-accent-custom-color "orange")
  (selected-window-accent-mode-style 'subtle))