Please switch from `zstd` to `zstandard` library. The latest one is more "officail"

[socketpair]

zstandard is widely considered the canonical Python binding for Zstandard, with feature completeness, strong maintenance, and community adoption.

Alternative modules like zstd are simpler, less featured, and often refer to zstandard as the superior option.

While not packaged inside the Facebook Zstandard C project, zstandard clearly occupies the role of the official (or de facto official) Python interface in the Zstd ecosystem.

Also, python 3.14 has built-in support for zstd.

So, the following changes are requested:

1. Make dependency on third-party library optional (for Python >= 3.14 it should not depend on any Zstd library)
2. Switch from zstd (https://pypi.org/project/zstd/) to zstandard (https://pypi.org/project/zstandard/)

What zstd author says:

And what chatgpt says (YES, I KNOW, IT MAY LIE):

[alisonatwork]

There is also backports.zstd available now for Python < 3.14: https://pypi.org/project/backports.zstd/

It's become particularly urgent to get this fixed because zstd no longer passes pip audit due to PYSEC-2023-121.