Consider avoiding eager imports where possible

> It seems that `launch_options` is intended to be a lightweight module, which is potentially contradicted by some of the imports here (not only the session class imports), and that might lead to concrete performance issues (for instance, at start-up). Should this be a concern? Perhaps it would be worthwhile looking into the preferred way to avoid eager imports if that's something we want/need to do. We could investigate that as a part of later work conducted by @mayankansys.

_Originally posted by @seanpearsonuk in [#4761](https://github.com/ansys/pyfluent/pull/4761/changes/ab34346aaf3824c48b11eb30d935d87a872ae6b1..c4f07326b25e443a20e10c7b9157112c1eeb9131#r2792274986)_