Feature/tfm

[arfazeli]

This PR adds an two-fluid model (TFM) for dispersed two-phase flow simulations.

Main features

• Implements TwoFluidModel with the B-TFM and C-TFM canonical formulations.
• Provides configurable interphase momentum-exchange (IME) closures:
  • drag
  • lift
  • virtual mass
  • laminar dispersion
• Supports phase-injection source terms, optional artificial diffusion, slope limiting, and lift deactivation near walls.
• Adds slip, zero-stress, zero-gradient, and zero-backflow boundary conditions.
• Adds a two-dimensional bubble-column example and tutorial.

Testing

Adds unit and full-system tests covering:

• TFM configuration and boundary conditions
• interphase closure behavior
• global mass conservation
• interphase action–reaction conservation
• manufactured-solution convergence