Rework session helpers

[PaulAsjes]

Description

Refactors the session helpers to add a new session class. The old helper methods will stay put, but we'll likely add a deprecation comment and remove them in a future major version.

See this gist as an example of how this would work in practise.

Documentation

Does this require changes to the WorkOS Docs? E.g. the API Reference or code snippets need updates.

[x] Yes

If yes, link a related docs PR and add a docs maintainer as a reviewer. Their approval is required.