Change MeaningsTable.target from a link to an object-reference attribute

[rly]

Summary

Changes MeaningsTable.target (common/table.yaml) from a link to an object-reference attribute (dtype with reftype: object, target_type: VectorData), matching VectorIndex.target and DynamicTableRegion.table.

# before
links:
- name: target
  target_type: VectorData
  doc: Link to the VectorData object for which this table provides meanings.

# after
attributes:
- name: target
  dtype:
    target_type: VectorData
    reftype: object
  doc: Reference to the VectorData object for which this table provides meanings.

Rationale

hdmf-common and nwb-schema use a consistent heuristic for the two mechanisms:

• Link points to a shared, standalone object owned elsewhere in the file, and possibly in another file since links can be external (e.g. Device, ImagingPlane, source TimeSeries).
• Object-reference attribute/dtype points to a co-located dataset from within table/column machinery (e.g. VectorIndex.target, DynamicTableRegion.table, electrodes.group, ImageReferences).

MeaningsTable.target is the second case: it points to a VectorData column of the same DynamicTable that owns the meanings group. The API in hdmf#1376 already enforces that the target must be a column of that table, so the target is inherently co-located and the link's only unique advantage, cross-file reach, does not apply. VectorIndex.target is the exact precedent: same target type, same name, same role of annotating a column of the same table, defined as an object reference.

The link in #91 was an unexamined default. The hdmf#1376 / #91 discussions were entirely about the BaseDynamicTable inheritance question; link vs. reference was never raised.

Changes

• common/table.yaml: MeaningsTable.target link -> object-reference attribute; reconcile docstrings ("linked" -> "referenced").
• common/namespace.yaml: bump hdmf-common to 1.10.0.
• docs/source/hdmf_common_release_notes.rst: add 1.10.0 entry.

Notes for reviewers

• This is a breaking change to the 1.9.0 MeaningsTable definition. I bumped the version to 1.10.0; adjust if you prefer a different number or want to fold it into a larger release. The release-notes date is left as "Upcoming".
• The corresponding API change in hdmf (hdmf/common/table.py) is not included here.

Verified the schema loads via HDMF 6.1.0 spec classes: target resolves to an attribute with dtype {'target_type': 'VectorData', 'reftype': 'object'} and MeaningsTable.links is empty.

PR checklist for schema changes

• Add release notes for the PR to docs/source/hdmf_common_release_notes.rst

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