isoformat() / fromisoformat() for datetime.timedelta

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-10-20.07:13:53.625>
labels = ['library', '3.10']
title = 'isoformat() / fromisoformat() for datetime.timedelta'
updated_at = <Date 2020-11-18.06:00:30.213>
user = 'https://bugs.python.org/ErikCederstrand'

bugs.python.org fields:

activity = <Date 2020-11-18.06:00:30.213>
actor = 'Erik Cederstrand'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-10-20.07:13:53.625>
creator = 'Erik Cederstrand'
dependencies = []
files = []
hgrepos = []
issue_num = 42094
keywords = []
message_count = 5.0
messages = ['379091', '379096', '379097', '381273', '381314']
nosy_count = 3.0
nosy_names = ['martin.panter', 'Erik Cederstrand', 'p-ganssle']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue42094'
versions = ['Python 3.10']