1047 beta limit

[stuartmuldrew]

Description

Closes #1047

Added beta limit from Tholerus et al. (2024) as iprofile option 6.

Checklist

I confirm that I have completed the following checks:

• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[chris-ashe]

New model has been implemented with suitable addition to the documentation