Add to/from string methods to datetime.timedelta

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-07-09.06:46:58.269>
labels = ['type-feature', 'library', '3.10']
title = 'Add to/from string methods to datetime.timedelta'
updated_at = <Date 2021-07-30.16:00:44.744>
user = 'https://github.com/tebeka'

bugs.python.org fields:

activity = <Date 2021-07-30.16:00:44.744>
actor = 'matthewkenigsberg'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-07-09.06:46:58.269>
creator = 'tebeka'
dependencies = []
files = []
hgrepos = []
issue_num = 41254
keywords = []
message_count = 5.0
messages = ['373380', '373400', '373439', '374017', '398564']
nosy_count = 6.0
nosy_names = ['tebeka', 'belopolsky', 'eric.smith', 'martin.panter', 'p-ganssle', 'matthewkenigsberg']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue41254'
versions = ['Python 3.10']