Use spec_helper where required

What does this MR do and why?

There were several instances where specs were failing as fast_spec_helper wasn't accessing the necessary classes.

Take 2 of !111969 (closed) with relevant commits cherry-picked.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #390552 (closed)