Allow a generic "state" specifier if step number is not available

This will remove the ability to filter by cycle, as step will need to increase monotonically until automatic cycle identification is added. This can be extended to ensuring that files can be read if no step column is available at all, in which case the data should be viewable, if not filterable.

No files, tests, or entry points are named. Start by locating the code that reads step columns and applies cycle or step filtering. Done means files without a step column remain viewable, while generic state filtering works with monotonically increasing steps and cycle filtering is removed until automatic cycle identification exists.

Written by the indexing model from the issue text.