Add ISO Basic format support to datetime.isoformat() and date.isoformat()

Feature or enhancement

Proposal:

In additional to the popular ISO 8601 Extended format, there's also an ISO 8601 Basic format for datetimes which is useful for filenames and URL components as it avoids characters such as eg. colon and is more compact. datetime.fromisoformat already supports parsing this format.

Example code:

datetime.isoformat(basic=True)
# 20240422T204705.335-0400
date.isoformat(basic=True)
# 20240422

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-120553

首先审查关联的 PR gh-120553 以及现有的 datetime.isoformat() 和 date.isoformat() 入口点。确认针对 datetime 和 date 提出的 basic=True 示例，包括紧凑偏移量和不存在分隔符，并验证所得行为已被覆盖，然后再考虑将 issue 视为完成。