Implement __repr__ for classes in csv module

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-06-05.16:54:02.928>
labels = ['type-feature', 'library', '3.10']
title = 'Implement __repr__ for classes in csv module'
updated_at = <Date 2020-06-05.16:54:02.928>
user = 'https://github.com/cool-RR'

bugs.python.org fields:

activity = <Date 2020-06-05.16:54:02.928>
actor = 'cool-RR'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-06-05.16:54:02.928>
creator = 'cool-RR'
dependencies = []
files = []
hgrepos = []
issue_num = 40875
keywords = []
message_count = 1.0
messages = ['370768']
nosy_count = 1.0
nosy_names = ['cool-RR']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40875'
versions = ['Python 3.10']