Add Reactant correctness check for AtmosphereModel.

[dkytezab]

Closes #683. Checking field equality before and after a single timestep.

[giordano]

Shouldn't run only on the GPU jobs? Also, it may be easier to move all these tests in a dedicate directory (reactant/?) and then in

Breeze.jl/test/runtests.jl

Lines 13 to 20 in d978c46

	if filter_tests!(testsuite, args)
	# Reactant compilation tests require --check-bounds=auto (Reactant/Enzyme
	# limitation).
	if !REACTANT_COMPAT
	delete!(testsuite, "reactant_centered_compilation")
	delete!(testsuite, "reactant_weno_compilation")
	end
	end

automatically filter out all the tests starting with reactant/. Edit: I went on and did that.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[dkytezab]

I believe that the errors here https://github.com/NumericalEarth/Breeze.jl/actions/runs/25581771362/job/75102082127?pr=687#step:11:536 are due primarily to EnzymeAD/Reactant.jl#2870. Basically, when we compile with Reactant, we alias the initial state rather than storing it as a copy, causing the RK3 substeps to be incorrect. This enters here

Breeze.jl/src/TimeSteppers/ssp_runge_kutta_3.jl

Lines 150 to 156 in 10c0d0b

	function store_initial_state!(model)
	U⁰ = model.timestepper.U⁰
	for (u⁰, u) in zip(U⁰, prognostic_fields(model))
	parent(u⁰) .= parent(u)
	end
	return nothing
	end

My workaround was instead to use a kernel to copy each of the prognostic fields, which I can implement now for the time being if that sounds good

There may also be an issue with maybe_prepare_first_time_step! that I need to investigate further.