Overview of CHIP NuttX Adaption

This platform is based on Linux adaptation, The code introduction can be seen in Linux's README.md:src/platform/Linux/README.md

To avoid integration errors caused by CI build breaks on the NuttX platform when new features are added to the Linux code, the current Linux code was copied as the base for NuttX to avoid a strong dependency between the two platforms.

The reason for adapting based on Linux is that NuttX is also a POSIX-compliant operating system, and the code can be almost completely reused while keeping the definitions and comments with the Linux prefix, which makes it easier to cherry-pick modifications from the Linux platform to the NuttX platform in the future.