Use minify_html instead of htmlmin

[danzou56]

Bug

#186

Behavex cannot be installed with python 3.13 because behavex depends on the remove cgi module via htmlmin to perform HTML minification.

Proposed solution

While the change to remove cgi from htmlmin is small, htmlmin hasn't been updated since Python 3.2/8 years ago, so it may not be reasonable to expect the maintainer to merge the pull request. Instead of relying on htmlmin, replace it with minify-html.

Behavex currently passes in pre and textarea as tags to exclude from minification. Likewise, minify-html does not remove whitespace in pre and textarea out of the box

• Docs make a specific call out to not altering whitespace in <pre> elements
• Tests show that whitespace is unaffected for pre and textarea elements (HTML entity 32 is a space character)