Cleanup surfaced once the oxlint config actually loads (no-unused-vars).
- drop dead locals/imports/params (cachedOffsetTop, elasticOut, key,
unused type imports, unused test imports; _-prefix unused mock params)
- createVirtualizer: keep the _version read (reactive subscription inside
$derived.by) but bind it to _v so it is not flagged
- scrollBreadcrumbsStore.test: keep the removeEventListener mock side
effect, drop the unread spy binding
Ilia Mashkov