[$] A FUSE implementation for famfs

The famfsfilesystem is meant to provide a shared-memory filesystem for large datasets that are accessed for computations by multiple systems. It wasdeveloped by John Groves, who led a combined filesystem andmemory-management session atthe 2025 Linux Storage, Filesystem, MemoryManagement, and BPF Summit (LSFMM+BPF) to discuss it. The session was afollow-up to the famfs session at last year'ssummit, 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 filesystemby using other kernel features.