Added support for gravity

[NasserFlexCompute]

Note

Medium Risk
Adds a new solver-translated Gravity volume model and extends the unit system with an acceleration dimension, which can affect parameter serialization/unit conversion and solver JSON generation. Also changes farfield ghost-surface naming (farfield→farField), which may break consumers relying on the old boundary name.

Overview
Adds gravity support for simulations. Introduces a new Gravity volume model (direction + acceleration magnitude, optional zone scoping) and exports it in flow360.__init__.

Extends units and solver translation to support gravity. Adds an acceleration dimension/unit to the unit system and exposed units, and updates the solver translator to non-dimensionalize gravity and emit a gravity block (global or per-zone). Includes new unit tests for model validation and translation.

Also aligns automated farfield boundary naming by changing the ghost surface from farfield to farField, and tweaks duplicate-entity validation to ignore models where entities is unset (None).

^{Written by Cursor Bugbot for commit c858176. This will update automatically on new commits. Configure here.}

[Copilot]

Copilot encountered an error and was unable to review this pull request. You can try again by re-requesting a review.

[cursor]

Cursor Bugbot has reviewed your changes and found 2 potential issues.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}

[cursor]

Farfield name change breaks registry pattern matching

High Severity

The GhostSurface name was changed from "farfield" to "farField", but simulation_params.py still uses the pattern "farfield" in _set_boundary_full_name_with_zone_name. The pattern matching in the entity registry uses case-sensitive regex (^farfield$), which won't match "farField". This means the farfield boundary's private_attribute_full_name will never be set, breaking boundary condition resolution for all users of AutomatedFarfield.