feat: add block tensor literal syntax for %op PPX extension Implement block tensor construction via list, tuple, and array syntax in %op blocks: [x1; x2] (output axis), (x1, x2) (input axis), [|x1; x2|] (batch axis). Disambiguate from ndarray constants by checking the first leaf expression. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>