Add support for using "tomllib" (in Python's stdlib since 3.11) and "tomli" TOML packages. They are preferred if they are found to be installed. But note that the declared dependency for the "toml" extra nevertheless is the "toml" package. Because it is available for all supported Python versions. So use Python 3.11+ or install "tomli" manually if you want to use the alternate packages.

# -*- coding: utf-8; mode: yaml; indent-tabs-mode: nil; -*-
%YAML 1.1
---

key1: in the root namespace
key2: in the root namespace -- too

tree1:
  key3: 0x20
  tree2:
    key4: get this as `tree1.tree2.key4'
    key5: true
    key6: 'off'