Stock lot product qty search

This module makes the Quantity field of Lot/Serial Numbers searchable, so users can find lots based on how much stock is actually available.

In the Lot/Serial Numbers screen, the search panel gains an "On hand" filter that shows only lots with a positive quantity. Users can also type quantity conditions (for example greater than, less than, equal to) in the search box.

The quantity is calculated from stock quants located in internal locations and in transit locations that belong to a company. Lots with no stock are treated as zero when the search condition includes zero, so they can still be found.

Only standard comparison operators are accepted; anything else raises an error, and the value searched must be a number. The module extends the stock.production.lot model and adds a search filter to the existing lot search view.