feat: move websocket-client to extra dependency

[akx]

Since websocket-client is only required when using websockets for attaching to containers (#62), I don't think it needs to be a required dependency.

This also bumps the minimum required version of websocket-client to that pinned by #3022.

[milas]

Thanks for the PR!

Out of curiosity, where/how are you using this library that you want to avoid the websocket-client dependency?

Technically, these changes look good. Thanks for the nice error message when it's not there. I'm not going to merge this right now, though: at a minimum, I want to do a major version bump along with this.

I'd also like to hear if others are interested in this (feel free to 👍🏻 this PR or comment with details), as it will potentially require a LOT of downstream consumers of this library to update their requirements.txt (or modern eqvuialent) since I think many do rely on websocket support when using the Engine API.

[akx]

@milas Hi, thanks for getting back on this! We have a situation where we'd like to avoid downloading extra dependencies in general – and from an attack surface/SBOM point of view, the less code there is, the better.

attach_websocket doesn't seem to be used all that much in the wild but sure, I agree this needs a version bump of some sort. #3126 would probably be nice to get in too at that point :)

[milas]

Merging this - I'm going to do a major version bump to v7 for Python 3.12 compatibility, as I had to remove some old functionality in the process that constitutes a breaking change, so it's a good time to accept this as well.

Thanks for the PR!

[akx]

@milas Great, thanks! Should v7 also drop Python 3.7 support? It's EOL date was 4 months ago.