Comparison Benchmark: C++ `std::bitset<256>`

The std::bitset<256> type in C++ is comparable to ByteSet.

ByteSet	std::bitset<256>
contains	test
insert	set
remove	reset
len	count
is_empty	none

Considerations:

• FFI overhead
  • No inlining

I think this is worth implementing and adding to https://github.com/nvzqz/byte-set-rs/issues/1.