[Feature]: Would very useful to have context graph metadata to have modified dates

### Feature Request

It would be really useful for blugin development for `context.project.graphs[graphRef.graphId].metadata` or the nodes `graph.nodes` to have date when that subgraph was last updated or modified.

i have caching in my plugin and i'd like to invalidate it when the grpah is updated.

As a workaround i'm doing a hash of `JSON.stringify(graph.nodes.map(m => m.data))`

### Code of Conduct

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