manifest: use tuple for `delta` in `fastdelta` This make the list content consistent and will help type annotation.

manifest: expose a version of the Class without interface decorator The decorator confuse Pytype. Having the "raw" python class exposed will also helps pytype when it get replaced by a native implementation. At least until we start using `typing.Protocol` in the future.

pytype: stop ignoring manifest.py pytype no longer complains about the file contents.

manifest: align some vfs option access on the fact we might not have options This make the usage consistent with the other option. Caught by pytype.