Issue with changing to default to fixed step size after event location

[jacobwilliams]

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If continuing the integration after an event location, and also changing from default to fixed-step size, there is a slight issue. In this case, there is a possibility that the specified step size is small enough that some number of the initial steps would prior to the last time reached. So, these need to be interpolated (and also checked for roots). Currently, these are omitted and it just takes the specified step.

See the note in ddeabm_with_event_wrapper_vec.