Beautiful Soup 4.12.1

[leonardr]

= 4.12.1 (20230405)

NOTE: the following things are likely to be dropped in the next
release of Beautiful Soup:

 Official support for Python 3.6.
 Inclusion of unit tests and test data in the wheel file.
 Two scripts: demonstrate_parser_differences.py and test-all-versions.

Changes:

* This version of Beautiful Soup replaces setup.py and setup.cfg
  with pyproject.toml. Beautiful Soup now uses tox as its test backend
  and hatch to do builds.

* The main functional improvement in this version is a nonrecursive technique
  for regenerating a tree. This technique is used to avoid situations where,
  in previous versions, doing something to a very deeply nested tree
  would overflow the Python interpreter stack:

  1. Outputting a tree as a string, e.g. with
     BeautifulSoup.encode() [bug=1471755]

  2. Making copies of trees (copy.copy() and
     copy.deepcopy() from the Python standard library). [bug=1709837]

  3. Pickling a BeautifulSoup object. (Note that pickling a Tag
     object can still cause an overflow.)

* Making a copy of a BeautifulSoup object no longer parses the
  document again, which should improve performance significantly.

* When a BeautifulSoup object is unpickled, Beautiful Soup now
  tries to associate an appropriate TreeBuilder object with it.

* Tag.prettify() will now consistently end prettified markup with
  a newline.

* Added unit tests for fuzz test cases created by third
  parties. Some of these tests are skipped since they point
  to problems outside of Beautiful Soup, but this change
  puts them all in one convenient place.

* PageElement now implements the known_xml attribute. (This was technically
  a bug, but it shouldn't be an issue in normal use.) [bug=2007895]

* The demonstrate_parser_differences.py script was still written in
  Python 2. I've converted it to Python 3, but since no one has
  mentioned this over the years, it's a sign that no one uses this
  script and it's not serving its purpose.