Brev: Use COPY --chmod to reduce Docker image layer count.

[brycelelbach]

Replace separate COPY + RUN chmod -R a+rwX steps with a single COPY --chmod=0777 in all tutorial dockerfiles and the stdpar docker-recipe, eliminating a redundant layer that duplicated the entire repo's file data.

$ brev/test-docker-image-sizes.bash compare --owner nvidia --tutorial accelerated-python --tag pull-request-157-latest --baseline main-latest
========================================
Image: ghcr.io/nvidia/accelerated-python-tutorial
========================================
  Current    (pull-request-157-latest)                11.83 GB
  Baseline   (main-latest)                            12.66 GB
  ────────────────────────────────────────────────────
  Change:  -850.48 MB (-6.56%)