feat: [#2387] option:checked matches a selected <option>

[marciomazza]

Description

Resolves #2387 — :checked is defined to match a selected <option>, not just a
checked <input>, but option:checked currently matches nothing in happy-dom.

const div = document.createElement('div');
div.innerHTML = `<select><option>a</option><option selected>b</option></select>`;
div.querySelectorAll('option:checked').length; // happy-dom: 0 — real browsers: 1

Root cause: SelectorItem.matchPseudoItem's checked case returns a match only
when tagName === 'INPUT', so an <option> always falls through to null.

Fix: the checked case now also returns a match for an OPTION element whose
selected is true.

Depends on #2268: without it, a cached option:checked result goes stale after a
programmatic selection change (option.selected / select.value /
select.selectedIndex) — the same cache-invalidation gap as #1594. The content
attribute path (selected) already clears the cache, so it is correct on its own.

Tests

Added 1 test in QuerySelector.test.ts: option[value='b']:checked is warmed with
nothing selected (0 matches), then setAttribute('selected', ''), then re-queried
and asserted to return the newly selected option — covers the new match and cache
freshness on the attribute path. Fails before, passes after. Full npm test passes.

AI

I used Claude Code to write this, over multiple iterations. I guided and reviewed
it myself at every step.

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Tests

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  • Ran the repro in Chrome (headless) console: option:checked warmed at 0 matches, then option.setAttribute('selected', ''), then re-query returns 1 element with value b. Matches the fixed behavior.
• Run the tests with npm test locally to make sure that all tests pass before submitting the PR.

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