Surface generator fix for diffusion

[dkachuma]

Fixes for the surface generator

• Replaces a relative time tolerance check with an absolute timeTolerance (1.0e-14) during rupture rate calculations, which prevents calculation errors or exceptions when a simulation uses negative start times.
• Adds logic to SurfaceGenerator::solverStep to retrieve the diffusion model and explicitly call initializeTemperatureState for the fracture subregions, ensuring properties like diffusivity and phase multipliers are correctly set up.

[Copilot]

Pull request overview

This PR fixes surface generation behavior when diffusion is enabled and improves robustness of rupture-rate calculations when simulations use negative start times.

Changes:

• Initialize diffusion state for fracture subregions during SurfaceGenerator::solverStep by retrieving the diffusion constitutive model and calling initializeTemperatureState.
• Replace a relative rupture-time tolerance check with an absolute timeTolerance to avoid divide-by-zero/invalid comparisons for negative rupture times.
• Move DiffusionBase::initializeTemperatureState from an inline no-op to a real implementation, and add a ConstantDiffusion override to initialize diffusivity state.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/coreComponents/physicsSolvers/surfaceGeneration/SurfaceGenerator.cpp	Initializes diffusion state for fracture subregions and uses an absolute time tolerance in rupture-rate computation.
src/coreComponents/constitutive/diffusion/DiffusionBase.hpp	Changes initializeTemperatureState from inline no-op to out-of-line virtual API.
src/coreComponents/constitutive/diffusion/DiffusionBase.cpp	Implements DiffusionBase::initializeTemperatureState to initialize phase diffusivity multipliers.
src/coreComponents/constitutive/diffusion/ConstantDiffusion.hpp	Declares an override for initializeTemperatureState.
src/coreComponents/constitutive/diffusion/ConstantDiffusion.cpp	Implements the override to initialize constant diffusivity values (and base multipliers).