feat: relax urllib3 requirements
The urllib3 library is heavily used by other packages and this package requires urllib3 >= 2.0.4. This is very new and breaks installing this package alongside many others, including Google authentication library.
Following the guidelines from urllib3 themselves, specify a requirement of "urllib3>=1.26,<3".
Additionally, freshen the API specifications which is required to allow CI tests to pass :(.
Edited by Dr Rich Wareham