[$] A FUSE implementation for famfs

The famfs filesystem is meant to provide a shared-memory filesystem for large data sets that are accessed for computations by multiple systems. It was developed by John Groves, who led a combined filesystem and memory-management session at the 2025 Linux Storage, Filesystem, Memory Management, and BPF Summit (LSFMM+BPF) to discuss it. The session was a follow-up to the famfs session at last year's summit, but it was also meant to discuss whether the kernel's direct-access (DAX) mechanism, which is used by famfs, could be replaced in the filesystem by using other kernel features.