fix(find): report a directory it cannot read and keep going (#414)

* fix(find): report a directory it cannot read and keep going

A readdir failure inside the traversal threw out of the batch, so one unreadable directory ended the whole search with no results. GNU find names the directory on stderr, continues, and exits 1 at the end. Every macOS home directory holds at least one such directory (.Trash), so a recursive find over one returned nothing.

* test(find): build the unreadable-directory fixture under /home/user like the rest of the suite

* fix(find): emit unreadable-directory messages in traversal order, from a fixed errno table

The message rides with its node as an effect, so several unreadable directories report in traversal order rather than in the order the parallel batch settled, and before the directory's own line under -depth. A failed read counts toward readdirCalls and readdirTime. Only the errnos a directory read can fail with are recoverable; a cancellation, an execution limit, or a policy refusal ends the search as it did. Adds the changeset.

* fix(find): keep the errno table in a Map, which the banned-patterns check asks of any keyed lookup