Detach definition of time grid from `Response` instances

Similarly to what has been implemented in LISA Orbits (https://gitlab.in2p3.fr/lisa-simulation/orbits/-/merge_requests/118) and in LISA Glitch (https://gitlab.in2p3.fr/lisa-simulation/glitch/-/merge_requests/65), we should detach the definition of the time grid (using sampling parameters t0, size, dt) from the Response` instance.

Concretely, we should remove these sampling attributes, as well as the equivalent init method's arguments; instead, a time array argument should be added to any function that computes a quantity on that grid.