feat(trade-in): validate active warehouse stock for trade-in serial numbers

[iamtalib13]

Summary

Added validation for Trade-In Serial Numbers to prevent receiving serial numbers that are already active in warehouse stock.

Changes

• Added validation in validate_trade_in_serial_no_and_batch.
• Checks whether the Trade-In Serial Number is already assigned to a warehouse.
• Checks whether the Serial No status is Active.
• Shows a user-friendly validation error on Sales Invoice save.
• Prevents duplicate stock creation during Trade-In.

Testing

1. Create an active Serial No assigned to a warehouse.
2. Create a Sales Invoice with Is Trade In enabled.
3. Enter the same Serial No in the Trade-In Serial No field.
4. Click Save.
5. Verify that validation error is displayed and the document is not saved.

Files Modified

• csf_tz/custom_api.py