Add the ability to use NetCDF

[simone-silvestri]

No description provided.

[Copilot]

Pull request overview

Adds optional NetCDF (NCDatasets-backed) output support to ClimaSeaIce by wiring in a Julia package extension, plus coverage in CI via a new NetCDF-focused test group.

Changes:

• Add ClimaSeaIceNCDatasetsExt extension to provide NetCDF output attributes for SeaIceModel.
• Add a NetCDFWriter integration test and hook it into runtests.jl under a new TEST_GROUP.
• Register NCDatasets as a weak dependency/extension trigger, bump package version, and add a dedicated CI job for the new test group.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ext/ClimaSeaIceNCDatasetsExt.jl	New extension module defining default NetCDF output attributes for sea-ice fields (and velocities).
test/test_netcdf_writer.jl	New test that runs a short simulation and validates NetCDF output contents.
test/runtests.jl	Adds a netcdf test group include.
Project.toml	Bumps version; adds NCDatasets weakdep/extension and adds it to test target.
.github/workflows/ci.yml	Adds a CI job to run only the netcdf test group.

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[Copilot]

Base.get_extension(Oceananigans, :OceananigansNCDatasetsExt) can return nothing. Defining function OCNE.default_output_attributes(...) will then error at extension load time (Nothing has no field default_output_attributes). Please either (a) extend a binding defined in the parent Oceananigans module (preferred), or (b) guard against isnothing(OCNE) before defining the method / provide a fallback.

Suggested change

	function OCNE.default_output_attributes(model::SeaIceModel)
	velocity_attrs = default_horizontal_velocity_attributes(model.grid)
	tracer_attrs = default_sea_ice_attributes()
	return merge(velocity_attrs, tracer_attrs)
	if !isnothing(OCNE)
	function OCNE.default_output_attributes(model::SeaIceModel)
	velocity_attrs = default_horizontal_velocity_attributes(model.grid)
	tracer_attrs = default_sea_ice_attributes()
	return merge(velocity_attrs, tracer_attrs)
	end

[glwagner]

indent