change enums.Device

[wanliAlex]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  We change enums.Device from inherited class to class

• What is the current behavior? (You can also link to an open issue here)
  enums.Device is a inherited class to class

class Device(str, Enum):
    cpu = "cpu"
    cuda = "cuda"

• What is the new behavior (if this is a feature change)?
  it is now a class with a custom __str__ method.

class Device(str, Enum):
    cpu = "cpu"
    cuda = "cuda"

    def __str__(self):
        # To pass the str(Device.cpu) == "cpu" check in clip
        return self.value

• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)

no

• Have unit tests been run against this PR? (Has there also been any additional testing?)
  no

• Related Python client changes (link commit/PR here)
  no

• Related documentation changes (link commit/PR here)
  no

• Other information:
  We change this due to an odd device check in clip models, which is
  str(Device.cpu) == "cpu", this will return False with inherited class.
  Therefore, we change it to class to solve the problem.

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added / updated (for bug fixes / features)

[pandu-k]

Does Device validation work with this change?