Unmatched ~ turns the rest of a paragraph into strikethrough #27

Reproduction

With tempest/markdown 1.2.2 on PHP 8.5.9:

$markdown = new \Tempest\Markdown\Markdown(null);
echo $markdown->parse('Duration: ~2h30.')->html;

Actual output:

<p>Duration: <s>2h30.</s></p>

Expected output:

<p>Duration: ~2h30.</p>

There is no closing ~, so the approximation marker should remain literal. The current StrikethroughRule::parse() consumes until ~ but appears to create a StrikethroughToken even when the closing delimiter is absent. This also occurs in ordinary prose such as about ~5 km.