feat: add addImportantToPseudoClasses option

[cossssmin]

Closes #383

Rules with pseudo-classes like :hover can't be inlined, so Juice keeps them in a <style> tag, but then the element's inlined styles win over them and the hover state never shows:

<style>.link { color: red; } .link:hover { color: green; }</style>
<a class="link">x</a>

The new addImportantToPseudoClasses option (off by default, as discussed in the issue) adds !important to the declarations in those rules:

<style>
.link:hover {
  color: green !important;
}
</style><a class="link" style="color: red;">x</a>

What it covers

• rules using a pseudo-class from juice.ignoredPseudos (:hover, :active, :focus, :visited, :link, plus any you add), also inside @media and nested &:hover
• every <style> tag in the output: preserved rules, style tags kept with removeStyleTags: false, removeInlinedSelectors mode, and preserved extraCss
• declarations that are already !important aren't doubled

What it leaves alone

• data-embed style tags
• pseudo-elements (::first-letter etc., also in the legacy :first-letter form), since inline styles don't override them
• the rest of the CSS: it's parsed without the nesting plugin and only rewritten when something changed

It runs as a single pass over the output's <style> tags at the end of juiceDocument, and costs nothing when the option is off.

Also available as --add-important-to-pseudo-classes on the CLI, typed in index.d.ts, and documented in the README's options table.

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