go-fuzz-dep: add bounds hints to serialization routines
go-fuzz-dep: add bounds hints to serialization routines

This can be considerably more efficient on LE machines,
since it allows the entire serialization routine
to be translated into a single (possible unaligned) read/write.

They also now match more closely the encoding/binary routines.

(Possible future work: Use the known type information during
instrumentation to dispatch directly to a specialized Sonar
routine.)

While we're here, add a note explaining why
these serialization routines have been copy-pasted.

dvyukov/go-fuzz,dvyukov/go-fuzz