Duplicate outputs in workflow2 due to Link object identity comparison #57

Issue

Duplicate Link objects appear in workflow2.outputs when the same section is referenced multiple times.

Location

simulationworkflowschema/general.py:237

The line if output not in self.outputs uses object identity comparison. Since Link doesn't implement __eq__, two Link objects with identical properties are not considered equal, allowing duplicates.

Example

Observed in VASP SinglePoint workflow:

workflow2.outputs = [
    Link(name="Output calculation", section="#/run/0/calculation/0"),
    Link(name="Output calculation", section="#/run/0/calculation/0"),  # duplicate
    Link(name="Output system", section="#/run/0/system/0")
]