Clean up retained Data/List Viewer state for obsolete Interactive outputs #1838

Background

This was identified during a ChatGPT-assisted review of #1835.

Interactive rich outputs retain R-side viewer state in .sess_env$dataviews so that notebook cells can continue paging or opening their full Data/List Viewer without serializing the complete object.

However, these states do not appear to be released when the corresponding Interactive output is no longer live.

For example, #1835 stores each plain list result with:

dataview_set_state(view_id, root)

and Interactive table outputs similarly retain Data Viewer state. Once an Interactive generation becomes archived, the extension correctly disables live controls, but the corresponding R-side state may remain referenced until the runtime itself is stopped.

This means old Interactive outputs can keep potentially large R objects alive even though they can no longer be browsed live.

Possible direction

Consider managing these states as Interactive-owned viewer resources, and dispose them when they can no longer be used, for example when:

• an Interactive generation is replaced or restarted;
• retained history is evicted;
• an Interactive session/output is otherwise permanently discarded.

This should probably cover both existing table outputs and the list outputs introduced in #1835 rather than adding list-specific cleanup.

The existing state_generation / dataview_dispose mechanism from #1741 may provide the appropriate foundation, but Interactive output retention and reconnect semantics need to be taken into account.