negative interval encoding issues due to python's timedelta implementation details

未指定源文件或测试。首先使用 asyncpg 0.29.0、Python 3.11.7 和 PostgreSQL 16.1 重现负三小时 timedelta 的情况，然后追踪 interval 的编码和解码行为。当预期的表示形式或有文档记录的变通方案得到确立，并且为负的子日 interval 提供回归覆盖时，即视为完成。

• asyncpg version: 0.29.0
• PostgreSQL version: 16.1
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: this is happening on local PG
• Python version: 3.11.7
• Platform:
• Do you use pgbouncer?: no
• Did you install asyncpg with pip?: yes
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?: yes

Python's timedelta implementation only allows to store negative number of days, hours, minutes, seconds, microseconds are always positive values. So when a negative value smaller than a day is interpreted it is stored in a strange way, example from Python's documentation:

Note that normalization of negative values may be surprising at first. For example:

>>> from datetime import timedelta
>>> d = timedelta(microseconds=-1)
>>> (d.days, d.seconds, d.microseconds)
(-1, 86399, 999999)

https://docs.python.org/3/library/datetime.html?highlight=timedelta#datetime.timedelta

In my particular case when I'm trying to store -3 hours, that's getting translated in python to:

datetime.timedelta(days=-1, seconds=75600)

And ends up stored in postgresql as: "0 years 0 mons -1 days 21 hours 0 mins 0.0 secs"

Is there also a workaround where I can skip timedelta for interval?