Make generated Client and AuthenticatedClient take an httpx.Timeout object optionally?

[mdlam92]

I find myself making a wrapper for the Client object to implement taking an httpx.Timeout object.

It would be cool if the generated Client objects took an float as it does today but also accepted the httpx.Timeout type for the timeout keyword argument.

httpx's Timeout is nice because it lets you configure specific timeouts for read/write/connect/global.

I'm willing to make the PR, wanted to gauge interest or if the maintainer will consider this before I go and do it.

[emann]

Should be a pretty simple change, just tweaking the type hints as far as I can tell. This may be better served waiting until #202 is implemented, however