testing – What is the relationship between IV & V professionals, testers and quality assurance engineers?

In the context of SDLC, I know that Verification AND VALIDATION is to check the deliverable input of the previous phase and to validate the output of the current one.
And this test is a phase among the SDLC phases.

Based on my research, I found in UToronto course notes:

V & V performed by a separate contractor

Which means that IV & V professionals are externally involved in the SDLC process and therefore have nothing to do with the test phase.

By cons, I find on another course that:

The test is the most common but not the only form of V & V

Which means that the testers are involved in IV & V.

This puzzles me as to whether the test phase and IV & V are performed by the same person (say a QA engineer) or if the people who perform IV & V are not involved in the testing phase.

Does the work of V & V professional exist in the software industry? What is the relationship between QA engineers, testers and IV & V?

How is the V & V process involved in project management: Is it running continuously within SDLC at the beginning or end?

Does the SDLC also include IV & V as a scene?