fix(batch): preserve references without object properties

[po-et]

Batch objects with properties=None currently omit the entire protobuf properties message, including explicitly supplied references. DataObject defaults to properties=None, so a reference-only object can be reported as inserted even though its links were never sent. This affects both synchronous and asynchronous insert_many and the shared batch encoder.

For a collection with a related reference property and an existing target UUID, this call drops the reference from the outgoing request:

collection.data.insert_many([DataObject(references={"related": target_uuid})])

Serialize the properties message when references are supplied, using an empty ordinary-property mapping when necessary. Objects with neither properties nor references keep their existing wire representation.

Validation

• Five regression cases fail on unchanged main: three protobuf round-trip cases and both public sync/async calls against a local mock gRPC server. The ordinary-property and empty-object controls already pass.
• With the fix, the affected unit and mock files pass all 33 tests. The complete offline test/ suite passes 550 tests with 1 skipped.
• Tests cover single UUID, UUID list and multi-target references, omitted/empty/populated properties and actual protobuf serialization. The public tests exercise real local HTTP/gRPC transport, with the database service simulated.
• Ruff 0.14.7 lint/format and Flake8 pass for all changed files. Project Pyright 1.1.400 reports 0 errors and 0 warnings with the isolated Python environment.

Validated on Python 3.12.12 / macOS arm64. A real Weaviate database, Docker integration suite and other platforms were not exercised. AI assistance was used for investigation, implementation and validation.

[orca-security-eu]

Orca Security Scan Summary

Status	Check	Issues by priority
Passed	Infrastructure as Code	0   0   0   0	View in Orca
Passed	SAST	0   0   0   0	View in Orca
Passed	Secrets	0   0   0   0	View in Orca
Passed	Vulnerabilities	0   0   0   0	View in Orca

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