fix(permissions): split comma-separated paths in --ignore-read (#35661)
The help text for `--ignore-read` advertises comma-separated paths the
same way `--allow-read`/`--deny-read` do
(`--ignore-read="/etc,/var/log.txt"`), but the parse site just did a
plain `.collect()` with no comma-splitting, so a comma-separated value
got stored as one literal string that never matches a real path — the
ignore rule silently does nothing. `--ignore-env` handles this correctly
via `use_value_delimiter`, which is what made `--ignore-read` stand out
as the inconsistent one rather than this being intentional.
Fixed it to go through `flat_escape_split_commas`, same as the adjacent
`allow-read`/`deny-read` blocks. Added a test covering the
comma-separated case.