feat: validate data paths in SatelliteDataModule initialization

[Alkholy53]

Validate data paths in SatelliteDataModule initialization

This PR addresses issue #18 by adding validation of data paths during the initialization of the SatelliteDataModule class.

Changes

• Added a new _validate_data_paths() method to check if all provided data paths exist
• Added validation call in __init__ after setting the zarr_path attribute
• Added proper error handling with descriptive messages

Testing

The changes ensure that invalid data paths are caught early during initialization rather than when the dataloader methods are called. This provides better error messages and prevents potential issues from surfacing later in the training process.

Impact

This change improves the robustness of the code by failing fast when data paths are invalid, making it easier to debug configuration issues.

[dfulu]

@Alkholy53 thanks for this, though it looks like your PR isn't passing some of the format checks