[Feature] Use refined Kconfiglib for improved rendering and configuration processing

Describe problem solved by the proposed feature

The Kconfiglib package available on PyPI is no longer actively maintained. In contrast, the fork at sysprog21/Kconfiglib enhances the TUI to align more closely with the Linux kernel’s menuconfig, fixes several bugs, and preserves full compatibility with the Kconfig language.

Describe your preferred solution

The screenshot below illustrates the improved TUI, including clearer window borders, drop shadows, and a functional scrollbar.

The screenshots below illustrate the improved user interface of guiconfig.py, bringing it closer to the professional standard of the Linux kernel’s qconf (make xconfig). In addition, it introduces dark/light theme switching for guiconfig, featuring a blue color scheme for consistent cross-platform styling.

The configurator can use the sysprog21/Kconfiglib package instead of the unmaintained Kconfiglib, while still processing all existing configurations correctly.

Describe possible alternatives

No response