Always redraw the `pdbpp` prompt on `SIGINT` during REPL use.

There was recent changes todo with Python 3.10 that required us to pin
to a specific commit in `pdbpp` which have recently been fixed minus
this last issue with `SIGINT` shielding: not clobbering or not
showing the `(Pdb++)` prompt on ctlr-c by the user. This repairs all
that by firstly removing the standard KBI intercepting of the std lib's
`pdb.Pdb._cmdloop()` as well as ensuring that only the actor with REPL
control ever reports `SIGINT` handler log msgs and prompt redraws. With
this we move back to using pypi `pdbpp` release.
