Implement the 3-phase Rachford-Rice solve

[dkachuma]

This pull request implements the 3-phase Rachford-Rice solve in preparation for 3-phase thermal models with K-values.

• Implements the constrained optimization approach originally by Michelsen, extended to the negative flash region as described by Leibovici and Nichita (2008).
• Formulates the problem as an unbounded minimization with linear constraints (hyperplanes) to ensure continuous differentiability at phase boundaries. The inner loop uses a bounded Newton-Raphson scheme coupled with an Armijo backtracking line search to ensure global convergence.
• Introduced parameterised unit tests in the new testRachfordRice3Phase.cpp file. This validates the solver across multiple mixture scenarios (ranging from 3 to 8 components), varied K-values, and tests both positive and negative phase fraction behaviour.