Make type for `nodeExtra` partial

[kirangadhave]

Currently the nodeExtra variable is typed as:

    type ProvVisConfig = {
        ...
        nodeExtra: Record<S, React.ReactElement | null>;
        ...
    }

We should make it partial like so: nodeExtra: Partial<Record<S, React.ReactElement | null>>;

This stops typescript from complaining that some keys are missing in case we decide that we want to skip extras for certain event types.

e.g. in persist I get this error: