Remove dead code in HumiditySimulation

[Copilot]

Addresses code review feedback on PR #271 identifying unused variable assignment in worldengine/simulations/humidity.py.

Changes

• Removed data = numpy.zeros((world.height, world.width), dtype=float) immediately overwritten by actual calculation
• Removed unused import numpy statement

# Before
import numpy
...
data = numpy.zeros((world.height, world.width), dtype=float)
data = (world.layers["precipitation"].data * precipitationWeight ...) / ...

# After
data = (world.layers["precipitation"].data * precipitationWeight ...) / ...

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