How to make CSS and JS both load in the footer
You can just add 'scope' option and pass either 'header' or 'footer' as the value.  

slick_carousel:
  css:
    theme:
      slick.min.css: { type: external, attributes: { aysnc: true }, scope:footer }
  js:
    slick.min.js: { type: external, minified: true, scope: footer }
  dependencies:
    - core/jquery