Replace matrix-client with matrix-nio

[YanWenKun]

The matrix-client 0.4.0 was released over three years ago and is working fine. However, it depends on urllib3~=1.21, while the latest version of urllib3 is 2.2.3.

At the moment, this isn't a pressing problem, as only a few packages (like PyGithub) require urllib3 and remain compatible with the older versions.

That said, I’m bringing this up in Discussions for awareness, though it's not urgent for the time being.

Additionally, the matrix-client recommends switching to matrix-nio as an alternative.

Lastly, thank you for your continued dedication and hard work!