Plural views view_files/view_cells; view_file stays as the Anthropic-style single-file form

[ncoop57]

Summary

Views take one or more targets under the plural name:

• view_files(*paths, ...): each file shown under a # file <path> header when several, with any line range applied to each file separately; a single path renders bare
• view_cells(path, *cell_ids, ...): same treatment with # cell <id> headers; replaces the view_cell function (the Notebook.view_cell method is unchanged)

view_file stays exactly as on main: the single-file form keeps the name and positional start_line/end_line established by Anthropic's text editor tool, which models have seen a lot. The editskill Naming section states both the plural rule and this exception.

Breaking change: the view_cell function is renamed to view_cells (no alias), and start_line/end_line are keyword-only on the plural views.

Changes

• nbs/12_tools.ipynb: view_files delegates per path to the unchanged view_file
• nbs/13_nbio.ipynb: single-cell rendering moves to _view_cell; view_cells loops *cell_ids (headers use resolved ids)
• fastcore/editskill.py: exports and Naming convention text updated

All new tests run red-green.

Note for review: this branch predates main's exec_cell/show_cell additions to 13_nbio.ipynb, so the regenerated nbio.py currently shows them as removed; merging main into the branch will clear that from the diff.