infoForNid method
Sticky info for nid, or null when the node is not currently
sticky. Hot-path lookup used by paint transform and retention checks.
Implementation
StickyHeaderInfo<TKey>? infoForNid(int nid) {
if (nid < 0 || nid >= _stickyByNid.length) return null;
return _stickyByNid[nid];
}