Fix shipment import parser source line tracking and sparse Excel parsing

[Ayush-3078]

Problem: The shipment import parser currently fails to accurately track source lines when encountering sparse data in Excel files, resulting in dropped records or incorrect data alignment.

Proposed Fix:

Update the parsing logic to correctly index empty Excel cells.
Ensure source line tracking synchronizes correctly with the parsed output.
Verify that all related data models are correctly updated.

[zhouj850]

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