Layer array input packages (READASARRAYS) not supported

[mjreno]

Grid input (e.g. RCHA) packages are currently not supported:

• test(rcha): support writing layer array input package #238
• Current failure is in structure.py structure_array(), which assumes list style formatted input, e.g. https://github.com/modflowpy/pyphoenix-project/actions/runs/18855284829/job/53801578235?pr=238
• Current test is formatting layer array based input as:

boundaries = np.full((20, 30), DNODATA, dtype=float)
for row in range(5, 15):
    boundaries[row, 0] = 100.0
for row in range(8, 12):
    boundaries[row, 29] = 95.0
for col in range(10, 20):
    boundaries[19, col] = 98.0

rch = Rcha(
    parent=gwf, recharge={0: boundaries}, print_input=True, save_flows=True, dims={"nper": 1}
)