cplxpair.m: Use tolerance that depends on Z to evaluate pairing (bug #45810). * cplxpair.m: Update docstring to explain how tolerance input is calculated. Validate TOL input is a positive scalar. Use standard code to find the first singleton dimension. When determing whether a conjugate pair exists, use a tolerance of TOL*eps (abs (z(i))). Use Octave coding convestions in BIST tests. Add BIST tests for tolerance input. Add BIST tests for input validation.