Re-implement binary arithmetic with `bit-ops` library

[thephoeron]

Both performance and accuracy can be significantly improved by re-implementing the binary arithmetic algorithms directly using the new bit-ops library. This will also make it easier to work with signed integers, and other arbitrary binary structures, encoded as bit-vectors.

CC: @guicho271828

[thephoeron]

See the Binary Arithmetic on Variable-Width Bit-Vectors project.