Make `PointReader` trait `Send`

[Mortano]

I'm trying to use the Reader type in a multithreaded context. However, Reader is not Send because the PointReader trait is not Send, which prevents any multithreaded usage as far as I can tell.

To the best of my knowledge, this would be doable by making the PointReader trait Send and adding explicit lifetime bounds on the Reader type (which at the moment assumes 'static lifetime). It would also require similar changes in the laz-rs crate to make LasZipDecompressor Send as well. I will open a similar issue in the laz-rs repository and link it here.

I implemented this in a fork which you can find here: https://github.com/Mortano/las-rs/tree/make-reader-send
With the necessary changes of the laz-rs crate here: https://github.com/Mortano/laz-rs/tree/make-decompressor-send

Let me know if this would be a sensible change, as at least the lifetime bounds on Reader seem to be a breaking change to me. It might also be worth discussion if these changes could be applied to the Writer trait as well.