Keyutils support

Redirect from https://github.com/hwchen/keyring-rs/issues/234

We have some use cases that we want to use keyring in linux without linux desktop in the first place. It then require our users to install the dbus properly. To solve the issue, I wrap the [rust implementation](https://github.com/hwchen/keyring-rs) which support keyutils with python bindings into https://github.com/unkcpz/keyringrs.

I guess to make it works with keyutils, it requires to directly interact with keyutils API? There are some python libraries I found which tries to support it but is not actively maintained:

- https://github.com/lilatomic/turkeyutils
- https://github.com/sassoftware/python-keyutils

There is one that is quite new which is also a rust wrapper but for keyutils directly:
- https://github.com/thorgate/python-linux-keyutils

Review the linked keyring-rs implementation and the listed Python keyutils wrappers first; the issue does not identify a keyring file or test entry point. Done means adding keyutils support for Linux use cases without requiring a desktop environment or D-Bus setup.

Written by the indexing model from the issue text.