Implement iterator specialization traits on more adapters This adds * `TrustedLen` to `Skip` and `StepBy` * `TrustedRandomAccess` to `Skip` * `InPlaceIterable` and `SourceIter` to `Copied` and `Cloned` The first two might improve performance in the compiler itself since `skip` is used in several places. Constellations that would exercise the last point are probably rare since it would require an owning iterator that has references as Items somewhere in its iterator pipeline. Improvements for `Skip`: ``` # old test iter::bench_skip_trusted_random_access ... bench: 8,335 ns/iter (+/- 90) # new test iter::bench_skip_trusted_random_access ... bench: 2,753 ns/iter (+/- 27) ```