feat: Add algebraic number polynomial and root-index extraction APIs

[toolCHAINZ]

Summary

For algebraic numbers (real roots of polynomials with rational coefficients), extract the
defining polynomial and the index of the root among the polynomial's real roots. Complements
the existing algebraic.rs which has arithmetic operations and comparisons but no way to
recover the underlying polynomial representation.

Z3 APIs

• Z3_algebraic_get_poly — extract the minimal polynomial whose root this algebraic number is
• Z3_algebraic_get_i — get the index of this root among the real roots of its polynomial
  (ordered from least to greatest)

Notes

• Both APIs are only meaningful on algebraic (non-rational) values; the high-level API should
  return Option or Result for inputs that are rational
• get_poly returns coefficients as a Vec<Real> (rational constants); the wrapper should
  expose this as a Vec<ast::Real>
• Together these two APIs allow fully reconstructing an algebraic number from its canonical
  representation, useful for interoperability with other CAS tools