Better preimages

[orkolorko]

A couple of issues with preimages

• RigorousInvariantMeasures.jl/src/Preimages.jl

  Line 183 in d04c374

  # TODO: there is probably a very clever general construction that can reduce `preimages`, `preimages_and_branches`,

  i.e., a general approach to preimages
• preimages for bases that need preimages of the endpoints, like NonPeriodicHat and Chebyshev