share_commodity_up set to 0 inactive

### What happened?

When applying a zero value to the parameter `share_commodity_up`, the value is ignored by GAMS and is therefore non binding. The reason for this is because there is no set `is_share_commodity_up` created which is used to handle 0 values in GAMS. The current workaround is to set the bound to a significantly small value which isnt 0 e.g. 0.000001.

### Code Sample

_No response_

### What did you expect to happen?

When adding a a `share_commodity_up` bound of 0, the respective technologies contributing to meeting the share constraint shouldnt have any activity.

### Versions

_No response_

### Additional Context

_No response_

Trace how GAMS handles the share_commodity_up parameter and compare it with analogous zero-value handling through is_share_commodity_up sets. Confirm that a bound of 0 is represented as binding and that technologies contributing to the share constraint have no activity, rather than requiring the small nonzero workaround.

Written by the indexing model from the issue text.