Box filter for integer scale factors, fixed-point area averaging otherwise.
The source view is bounds-checked so a short or misdescribed PipeWire buffer
is reported instead of read out of range.
The PipeWire thread publishes into a single slot and the network thread takes
from it, swapping buffers instead of copying so the steady state does not
allocate. An older pending frame is dropped when a newer one arrives.
The .fbs files come from HyperHDR (see schema/NOTICE); the *_generated.rs
files are flatc output regenerated by scripts/regen-fbs.sh, which refuses to
run unless flatc matches the pinned flatbuffers crate.
oleksandr