PERF use regular expression in format_is_iso?

[MarcoGorelli]

Suggested here: #50242 (comment)

Here are the relevant lines of code:

pandas/pandas/_libs/tslibs/parsing.pyx

Lines 821 to 838 in 4e88c3f

	def format_is_iso(f: str) -> bint:
	"""
	Does format match the iso8601 set that can be handled by the C parser?
	Generally of form YYYY-MM-DDTHH:MM:SS - date separator can be different
	but must be consistent. Leading 0s in dates and times are optional.
	"""
	iso_template = "%Y{date_sep}%m{date_sep}%d{time_sep}%H:%M:%S{micro_or_tz}".format
	excluded_formats = ["%Y%m%d", "%Y%m", "%Y"]
	for date_sep in [" ", "/", "\\", "-", ".", ""]:
	for time_sep in [" ", "T"]:
	for micro_or_tz in ["", "%z", ".%f", ".%f%z"]:
	if (iso_template(date_sep=date_sep,
	time_sep=time_sep,
	micro_or_tz=micro_or_tz,
	).startswith(f) and f not in excluded_formats):
	return True
	return False

[ShashwatAgrawal20]

take