Fix s3.get_subdevices()

[felipediel]

Context

Bug report: #754.

Proposed change

Improve s3.get_subdevices() logic:

• Make "step" a parameter;
• Use a set to ignore duplicate devices;
• Leverage on resp["total"] to break the loop before the time (more efficient);
• Improve logic if len(seen) == total -> if len(seen) >= total.

Thanks @stevendodd!

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New device
• New product id (the device is already supported with a different id)
• New feature (which adds functionality to an existing device)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests
• Documentation

Additional information

• This PR fixes issue: fixes #
• This PR is related to:
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• The code has been formatted using Black.
• The code follows the Zen of Python.
• I am creating the Pull Request against the correct branch.
• Documentation added/updated.