We need a lock‑free MPMC bitset to support future event/waitset work where many producers can signal events…

We need a lock‑free MPMC bitset to support future event/waitset work where many producers can signal events…: a task in LegoFlow-SWE (Harbor dataset). Two public types are required: BitSet (runtime‑sized) and FixedSizeBitSet<const CAPACITY: usize (compile‑time‑sized). Both must provide: