Some users may accidentally supply PMFs that are longer than the observed data (or intentionally in some rare settings). In theory this should be handled internally by slicing them to match the maximum length but in practice (i.e. #735) this may lead to issues. Even if this is working as intended we likely want to warn the users that this is happening vs doing it automatically.

We likely want to make this warning once per session so as not to annoy advanced users who want this functionality.