Docments from Annotated metadata and NumPy docstrings, callable truncstr suffixes, shared preview rows

[jph00]

docments reads parameter docs from source comments, Annotated metadata, and NumPy docstrings through one path, and docstring/get_source see through partials, wrappers, and callable instances. apisurface.mk_sig puts parameter descriptions into Annotated so generated APIs document themselves the same way.

truncstr accepts a callable suf that receives the number of characters cut. New nbio.prev_line is the preview row shared by CellRow and aidialog: a cut row shows the node's size before its separator and ends with the missing count.

Also: untar_dir with uid/gid handles dangling symlinks, and notebook validation requires cell metadata to be a dict.