TST: Review ``_assert_within_tol`` positional arguments
TST: Review ``_assert_within_tol`` positional arguments

``_assert_within_tol`` is often called with positional
 arguments that end up being filled into the signature,
 e.g. calls to ``_assert_within_tol(Y1, Y2, eps, verbose > 2)``
 evaluate to calls where `atol=eps` and `rtol=verbose > 2`.

 This PR converts calls to using keywords where needed. Further
 it modifies some tolerances to be stricter.

WarrenWeckesser/scipy,mdhaber/scipy,vigna/scipy,endolith/scipy,WarrenWeckesser/scipy,rgommers/scipy,anntzer/scipy,tylerjereddy/scipy,tylerjereddy/scipy,WarrenWeckesser/scipy,WarrenWeckesser/scipy,perimosocordiae/scipy,rgommers/scipy,anntzer/scipy,zerothi/scipy,endolith/scipy,mdhaber/scipy,endolith/scipy,zerothi/scipy,anntzer/scipy,andyfaff/scipy,perimosocordiae/scipy,anntzer/scipy,vigna/scipy,perimosocordiae/scipy,mdhaber/scipy,mdhaber/scipy,rgommers/scipy,tylerjereddy/scipy,perimosocordiae/scipy,WarrenWeckesser/scipy,zerothi/scipy,zerothi/scipy,tylerjereddy/scipy,rgommers/scipy,Stefan-Endres/scipy,zerothi/scipy,andyfaff/scipy,vigna/scipy,vigna/scipy,scipy/scipy,scipy/scipy,mdhaber/scipy,andyfaff/scipy,rgommers/scipy,vigna/scipy,endolith/scipy,anntzer/scipy,scipy/scipy,Stefan-Endres/scipy,ilayn/scipy,scipy/scipy,endolith/scipy,andyfaff/scipy,ilayn/scipy,ilayn/scipy,ilayn/scipy,perimosocordiae/scipy,WarrenWeckesser/scipy,zerothi/scipy,Stefan-Endres/scipy,andyfaff/scipy,Stefan-Endres/scipy,ilayn/scipy,Stefan-Endres/scipy,ilayn/scipy,tylerjereddy/scipy,scipy/scipy,perimosocordiae/scipy,anntzer/scipy,Stefan-Endres/scipy,mdhaber/scipy,andyfaff/scipy,scipy/scipy,endolith/scipy