Fix: compile closest() selectors once per document in the static scanner (#575) (#595)

StaticElement.closest() handed the raw selector string to css-select's
is() on every ancestor step, recompiling the same selector N times for
an element N levels deep. StaticDocument now caches one compiled
matcher per selector (failed compiles cached as rethrowers so bad
selectors still return null). Findings are byte-identical across the
fixture corpus; scan time drops to ~62% on the fixtures and ~7x faster
on deep-DOM pages.

Prepared with AI assistance (Cursor agent), directed by @abdulwahabone.

Co-authored-by: Cursor <cursoragent@cursor.com>

cli/engine/engines/static-html/detect-html.mjs

@@ -134,7 +134,7 @@ async function detectHtml(filePath, options = {}) {
         parseDocument: htmlparser2.parseDocument,
         selectAll: cssSelect.selectAll,
         selectOne: cssSelect.selectOne,
-        is: cssSelect.is,
+        compile: cssSelect.compile,
         csstree,
         domutils,
       };