Consolidate cartesian interp option and introduce structured SimulationResult return

[faridyagubbayli]

I removed the duplicate cart_interp option and kept cartesian_interp to make the API clear and consistent, then switched the executor return from a loose dotdict to a typed SimulationResult. This cuts confusion around options, improves IDE help and readability, and makes it safer and simpler to work with outputs from the k‑Wave binaries.

Changes

• kwave/options/simulation_options.py: removed cart_interp, kept cartesian_interp, cleaned docs/validation.
• tests/test_tvsp_3D_simulation.py, tests/test_ivp_3D_simulation.py: switched to cartesian_interp.
• kwave/data.py: added SimulationResult dataclass (+ from_dotdict).
• kwave/executor.py: return SimulationResult from run_simulation.
• kwave/kspaceFirstOrder2D.py, kwave/kspaceFirstOrder3D.py, kwave/kspaceFirstOrderAS.py: updated return annotations/imports.
• tests/test_executor.py: assertions now expect SimulationResult.

Compatibility

• Non-breaking at call sites; return type is now structured. Consumers relying on dict-like access should migrate to attributes.

Tests

• Updated unit tests pass locally; basic import/creation of SimulationResult verified.

Summary by CodeRabbit

• Breaking Changes

  • SimulationOptions parameter renamed from cart_interp to cartesian_interp (update call sites).

• New Features

  • Simulation solvers now return a structured SimulationResult object consolidating grid info and arrays for pressure, velocity, and intensity.

• Tests

  • Tests updated to expect and validate the new structured SimulationResult outputs.