controllers: ControllerRunner reconnect loop refactor

This issue follows my comment on https://github.com/DiamondLightSource/fastcs/pull/420#issuecomment-5513087608 and the comment reply (https://github.com/DiamondLightSource/fastcs/pull/420#issuecomment-5517145387). This issue should be added as a sub-issue of https://github.com/DiamondLightSource/fastcs/issues/388, renamed appropriately, and this issue comment should be amended appropriately with the issue details. The attached markdown file is the proposed solution to resolve the two linked comments.

[controller-lifecycle-design(1).md](https://github.com/user-attachments/files/31831715/controller-lifecycle-design.1.md)

Start by reading the comments on pull request 420 and the proposed controller-lifecycle-design(1).md attachment, then review the parent issue 388 for context. The issue also calls for renaming it, making it a sub-issue of 388, and amending its comment; done means the reconnect-loop refactor and those issue-organization updates match the agreed design.

Written by the indexing model from the issue text.