Add typed table constraints to DynamicTableRegion columns in ecephys, misc, and ophys

[ehennestad]

Summary

Several DynamicTableRegion columns across the core schema carry no table attribute specifying which table they reference. By contrast, the icephys relational tables (SimultaneousRecordingsTable, SequentialRecordingsTable, etc.) do declare typed table constraints via a dtype refspec on the table attribute. This inconsistency means the schema cannot validate that these region columns point to the correct table.

Affected fields

File	Type	Field	Suggested target type
nwb.ecephys.yaml	ElectricalSeries	electrodes	ElectrodesTable
nwb.ecephys.yaml	FeatureExtraction	electrodes	ElectrodesTable
nwb.misc.yaml	Units	electrodes	ElectrodesTable
nwb.misc.yaml	DecompositionSeries	source_channels	ElectrodesTable ??
nwb.ophys.yaml	RoiResponseSeries	rois	PlaneSegmentation

Current icephys pattern (for reference)

The icephys relational tables use a typed table attribute with a dtype refspec to enforce the target table type. This is the pattern that should be adopted here for consistency.

Open questions

• Does source_channels in DecompositionSeries have a well-defined target table to constrain to?

[oruebel]

This makes sense to me. There could be some issue with compatibility of older files, but I think this linking was mostly enforced in the APIs for the above cases (aside from `DecompositionSeries).

Does source_channels in DecompositionSeries have a well-defined target table to constrain to?

The original motivation for DecompositionSeries was electrical recordings, however, I think it is a more generic type and could be used for other data as well. I.e., it could make sense to leave DecompositionSeries.source_channels untyped. We should discuss. The other proposed refinements of types sound reasonable to me.