fix: pos item price in get_item and item search

[diptanilsaha]

Changes include:

• Replaced get_doc method with SQL to fetch Item UOMs.
• If Item is searched using Serial Number, it should only display the Item Price for the Item's stock_uom.
• Changed the logic to display the item prices based on the availability of the item's sales_uom and stock_uom. If item Prices are not available for either UOM, it will show the Item Price for what is available, provided that the UOM exists in the Item's uoms.