bv: Unify bit-blasting code for udiv and urem. (#7188)

bv: Unify bit-blasting code for udiv and urem. (#7188)

This refactor additionally removes the caching for urem/udiv cases when
bit-blasting udiv/urem and eliminates the only rewrite() calls in the
bit-blaster. Caching is not required since repeated calls to udiv/urem
with the same arguments will produce the same circuit. Further, the rewrite()
calls during bit-blasting would further complicate the recording of
bit-blasting proofs and hence is removed.