deps: use msgpackr

[justinmk]

Evaluate if it's worth switching to https://www.npmjs.com/package/msgpackr instead of our current msgpack dependency.

• See https://github.com/neovim/node-client/pull/207#issuecomment-1637067789
• Previous: https://github.com/neovim/node-client/issues/78
• Related: https://github.com/vscode-neovim/vscode-neovim/issues/1316

[gjf7]

It appears that msgpackr does not support using 0 as an extension type code. https://github.com/kriszyp/msgpackr/issues/150

[justinmk]

Thank you for mentioning that. Arg, I really wish we hadn't played with "extension types".