GEOPY-2994: Support Grid2D in grid_model_merger application

[domfournier]

GEOPY-2994 - Support Grid2D in grid_model_merger application

[Copilot]

Pull request overview

Adds Grid2D support to the grid_model_merger application by extending mesh conversion utilities and adapting the merge driver to build a 2D output grid when the first selected grid is Grid2D.

Changes:

• Add Grid2D ↔ discretize.TensorMesh conversion helpers and extend shared utilities to handle 2D meshes.
• Update grid_model_merger driver/options to accept Grid2D inputs and emit Grid2D outputs when appropriate.
• Expand test coverage to include Grid2D merge cases and mixed-type merge parameterization.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/run_tests/octree_creation/run_test.py	Adds explicit horizon flags in curve refinement test inputs.
tests/run_tests/grid_model_merger_test.py	Adds Grid2D merge tests and parametrized mixed-type merge tests.
grid_apps/utils.py	Introduces Grid2D conversion helpers and adapts utilities for 2D discretize meshes.
grid_apps/grid_model_merger/options.py	Allows Grid2D selections by converting to discretize meshes via grid2d_to_tensor.
grid_apps/grid_model_merger/driver.py	Builds 2D output grids for Grid2D merges and updates global mesh spec handling.

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