Streamdeck

- Added new `set_poll_frequency()` function.
- Added new `is_open()` function.
- Fixed a possible internal thread join error when a deck object was closed.

- Add support for the new StreamDeck MK2.

- Updated animated example script to attempt to maintain a constant FPS, regardless of rendering time.
- Fixed a race condition in the LibUSB HIDAPI transport backend that could cause crashes when a device was closed.

- Altered LibUSB transport workaround to only apply on Mac.
- Fixed internal _extract_string() method to discard all data after the first NUL byte, fixing corrupt serial number strings being returned in some cases.
- Set minimum Python version to 3.8, as some of the library uses newer syntax/core library features.

- Added new ``PILHelper.create_scaled_image()`` function to easily generate scaled/padded key images for a given deck.
- Updated LibUSB transport backend so that device paths are returned as UTF-8 strings, not raw bytes.
- Updated version/serial number string extraction from StreamDecks so that invalid characters are substituted, rather than raising a ``UnicodeDecodeError`` error.
- Added LibUSB transport workaround for a bug on Mac platforms when using older versions of the library.

- Fixed memory leak in LibUSB HIDAPI transport backend.