Replace the stub factor_n_sqf_pp (TODO: invoke Dejan's procedure) with a
working implementation using bivariate Hensel lifting:
- Evaluate away extra variables to reduce to bivariate
- Factor the univariate specialization
- Lift univariate factors to bivariate via linear Hensel lifting in Zp[x]
- Verify lifted factors multiply to original over Z[x,y]
- For >2 variables, check bivariate factors divide the original polynomial
Tests: (x0+x1)(x0+2x1)(x0+3x1) now correctly factors into 3 linear factors.
All 89 unit tests pass in both release and debug builds.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
