Moving electrical panel. Do I need to rewire all circuits?
Yes.  I fit steel junction boxes in places the old wires can reach.  Then run EMT conduit between the panel and those boxes.  No more than 3 circuits (MWBC counts as 1) in each conduit and use 3/4" conduit, for easy pulling and future expansion. NEC limits each conduit run to 9 conductors (4 circuits: grounds and MWBC neutrals do not count) unless you upsize conductors.  I'd use the biggest boxes I can get, no smaller than deep 4" 2-gang boxes, because they will be full of splices.   I use THHN/THWN through the conduit to the panel.  Terminate grounds at the ground lug in the junction box, or run a wire. EMT is a ground path.

But try this.  Leave the panel where it is, and install a sub-panel in public or tenant space.  In fact, forward-think: if in the future you wanted to set up the tenant with a separate meter, what could you do now (cheaply) that would make that cheaper and easier later?   Setting them up with a sub-panel easily converted into a new main panel, would be awesome all around.   This isn't necessarily a large investment, mostly just forethought to not paint yourself into a corner.

Honestly I'm surprised your GC is trying to feather-bed the project with unneeded work when the sub-panel is a really worthy effort.