ipaddress.reverse_pointer returns nonsense if prefixed input is given

Bug report

ipaddress.reverse_pointer does not seem to validate its input at all. For example:

$ python3
Python 3.10.4 (main, Apr  2 2022, 09:04:19) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ipaddress
>>> ipaddress.ip_network('2001:db8:1:2:3:4:5::/64',False).reverse_pointer
'4.6./.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa'
>>> 

This is very obviously wrong.

In this case of prefixed input, the output should be cut to the appropriate prefix length, yielding
2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa as output. It is ok to assume /128 as the default, converting 2001:db8:1:2:3:4:5:: to 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.0.1.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa, but input longer than that is an error.

Prefixed address strings are for example important when generating zone names for the server side of IPv6 reverse DNS. Run-of-the-mill network client software is unlikely to use this for addresses shorter than /128, but for the server side it is an important use case.

Greetings
Marc

首先运行报告中的 Python 重现程序，并跟踪 ipaddress.reverse_pointer 入口点，以了解带前缀的输入是如何处理的。完成标准是：带前缀的 IPv6 输入生成按其前缀长度截短的反向指针名称，默认的不带前缀输入按 /128 处理，并拒绝长于 /128 的输入。