fix(client): thread connection limits into the sync transport

[rkruze]

No description provided.

[pushrax]

looks like this broke as of #111

there's some other httpx settings that aren't passed through, and might be worth doing, but we could wait for a use case (e.g. http1 vs http2 settings, cert verification settings)

[benesch]

there's some other httpx settings that aren't passed through, and might be worth doing, but we could wait for a use case (e.g. http1 vs http2 settings, cert verification settings)

I'll just do it now while it's on our minds: #255