Changes:
* Support python 3.12 (PR https://github.com/vxgmichel/aiostream/pull/93)
* Support pyright and improve typing in general (PR https://github.com/vxgmichel/aiostream/pull/99)
* Move from `setup.*` to `pyproject.toml` (PR 101, 102, 103, 110)
* Add typing to `aiostream.test_utils` (PR 104)
* Make operators a singleton object instead of a class (PR 106)
* Add sources operator to fix a [breaking change in v0.5.x](https://github.com/vxgmichel/aiostream/releases/tag/v0.5.0) (PR #108, issue 95)
Thanks to hf-kklein for the valuable contributions :)