Optimised io.datafind.find_frametype for multiple channels
This PR introduces a rewrite of the gwpy.io.datafind.find_frametype
method to support searching for matching types for multiple channels. TimeSeriesBaseDict.find
has been patched to use this new functionality, which should greatly speed up multi-channel finds.
The logic in the new find_frametype
looks very complicated, but hopefully the inline comments are enough to help readers understand the flow.