FUTEX2 NUMA & Small Futexes Revived For Linux

Back in 2020~2021 there was lots of talk and work around FUTEX2 for improving the Linux kernel's Futex implementation for fast user mutex. The FUTEX2 work was driven in large part for helping Steam Play / Wine gaming by better matching the behavior of Microsoft Windows with its WaitForMultipleObjects handling. While the initial code landed back in Linux 5.16, there's been other remaining FUTEX2 features still desired like variable-sized futexes and NUMA-awareness. Finally now we're seeing that work revived...