Refactor Skyrim interface for enhanced forecasting

[m13uz]

• Merged with #21
• Fixed typo in requirements.txt
• Refactored Skyrim’s interface to enable generating full forecast data array for selected channels, Skyrim.forecast()
• Updated generate_dataset.py downstream (@efesurekli)

Nothing changed for the Skyrim.predict() method

from skyrim.core import Skyrim
import datetime

model = Skyrim("pangu", ic_source="cds")
start_time = datetime.datetime(2024, 5, 1)

# Forecast with 2 steps
pred_da = model.forecast(start_time, n_steps=2)
print(pred_da.shape)  
# Output: 
# (3, 69, 721, 1440)

# Forecast with 8 steps for specific channels
pred_da = model.forecast(start_time, n_steps=8, channels=["u10m", "v10m"])
print(pred_da.shape)  
# Output: 
# (9, 2, 721, 1440)

print(pred_da.channel.values)
# Output: 
# ['u10m' 'v10m']

print(pred_da.time.values)  
# Output:
# ['2024-05-01T00:00:00.000000000', '2024-05-01T06:00:00.000000000',
#  '2024-05-01T12:00:00.000000000', '2024-05-01T18:00:00.000000000',
#  '2024-05-02T00:00:00.000000000', '2024-05-02T06:00:00.000000000',
#  '2024-05-02T12:00:00.000000000', '2024-05-02T18:00:00.000000000',
#  '2024-05-03T00:00:00.000000000']