Stop using undocumented Python function sre_parse.parse_template()

[goodmami]

PyDelphin currently uses sre_parse.parse_template() for parsing the capturing groups of regular expressions:

pydelphin/delphin/repp.py

Lines 634 to 636 in 33415cf

	def _get_segments(replacement: str, _re):
	# parse_template() is an undocumented function in the standard library
	groups, literals = parse_template(replacement, _re)

These are deprecated as of 3.11:

python/cpython#91308

A stopgap solution is to change the import from sre_parse to re._parser, similar to what Lark did: lark-parser/lark@1b62465

This could be the reason tests are failing for Python 3.12.

[goodmami]

This could be the reason tests are failing for Python 3.12

Not entirely. This is the risk of using non-public functions. In Python 3.12, an optimization was made to re.sub() (see python/cpython#91524) which involved a change in the shape of the return value of parse_template().