Compare enums by identity

[MicaelJarniac]

Enumeration members are compared by identity
~ Enum docs for Python 3.8 and 3.12

The doc does mention, though:

Warning

It is possible to reload modules – if a reloaded module contains enums, they will be recreated, and the new members may not compare identical/equal to the original members.

So I'm not entirely sure my suggestion won't break something if that's happening.

Some instances of comparisons by equality here:

• httpx/httpx/_client.py

  Line 203 in 7df47ce

  return self._state == ClientState.CLOSED

• httpx/httpx/_client.py

  Line 913 in 7df47ce

  if self._state == ClientState.CLOSED:

This is a minor suggestion, and I understand if this is not wanted.