Some detector refactoring and tests update

• Now uses mocks in the detector tests to mock away the utils functions (i.e. the tests will no longer depend on changes in utils).
• Also introduces a mock for a waveform generator test for the same reason
• Consolidates setting of start_time, duration, sampling_frequency in InterferometerStrainData into a separate method.
• Refactored infer_time_domain_dependence and infer_frequency_domain_dependence to reduce the amount of redundant code.
• Otherwise just some formatting

Sorry that this assortment of changes is a bit random. I salvaged stuff together from 3 different branches, where I was trying things.