[tools.quadratures] make returned matrices read only
[core.cache] make memory cached arrays read only
[operators.fv] rename EngquistOsherFlux->SimplifiedEngquistOsherFlux
[operators.fv] add EngquistOsherFlux
[operators.fv] rename nonlinear_advection_engquist_osher_operator->nonlinear_advection_simplified_engquist_osher_operator
[operators.fv] add nonlinear_advection_engquist_osher_operator
[discretizers.advection] update