Added a new script to generate a mask without rivers

[spiani]

No description provided.

[Copilot]

Pull request overview

This PR introduces a new mitgcm_inputs cosmetic_mask subcommand to generate a “cosmetic” meshmask with river cells removed (optionally in a MER/CF-compliant NetCDF layout), wires it into the main CLI entrypoint, and updates the MER statics launcher to produce/use that mask.

Changes:

• Added cosmetic_mask CLI command to build a river-free mask and write it to NetCDF (with optional --mer output format).
• Registered the new command in src/mitgcm_inputs/__main__.py so it’s available via poetry run mitgcm_inputs cosmetic_mask ....
• Updated the MER statics generation script to create cmeshmask.nc (or copy meshmask.nc when no rivers).

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/mitgcm_inputs/cosmetic_mask/__init__.py	New cosmetic mask command implementation and CLI argument definitions.
src/mitgcm_inputs/__main__.py	Registers the new subcommand and updates FLUXES executor naming.
launcers/all_statics/generate_mer_statics.sh	Generates cmeshmask.nc and passes options to downstream commands.
poetry.lock	Dependency lockfile updated (Poetry version + resolved deps).

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