Milvus client/v2.6.5 release notes

Adds Go SDK support for nullable vector columns across dense, binary, sparse, and int8 vector types.
Adds Array field partial update helpers for ARRAY_APPEND and ARRAY_REMOVE in upsert requests.
Validates that vector fields added to existing collections are nullable before sending AddCollectionField requests.
Bumps the Go SDK version constant to 2.6.5 and updates milvus-proto/go-api/v2 to v2.6.17.

Nullable vector columns: Added nullable column constructors for vector fields: NewNullableColumnFloatVector, NewNullableColumnBinaryVector, NewNullableColumnFloat16Vector, NewNullableColumnBFloat16Vector, NewNullableColumnInt8Vector, and NewNullableColumnSparseFloatVector. These constructors accept compact non-null vector values plus validData, and validate that the values length matches the valid row count. (#49848)
Nullable vector response decoding: FieldDataColumn now decodes nullable vector field data using ValidData for FloatVector, BinaryVector, Float16Vector, BFloat16Vector, SparseFloatVector, and Int8Vector. Null rows are preserved in the returned column while compact wire-format vector payloads are expanded back to row-aligned columns. (#49848)
Array partial update operations: Added upsert helpers WithArrayAppend(fieldName), WithArrayRemove(fieldName), and WithFieldPartialOp(fieldName, op) for Array field partial updates. Non-REPLACE field ops are serialized into UpsertRequest.FieldOps and automatically enable partial_update for both column-based and row-based upserts. (#49328)

AddCollectionField vector validation: AddCollectionField now validates options before sending the RPC and rejects vector fields added to existing collections unless the field is marked nullable=true, preventing invalid schema changes from reaching the server. (#49848)
All-null sparse vector handling: Sparse vector column serialization now handles empty value sets by emitting dimension 0, allowing all-null nullable sparse vector columns to round-trip without panics or invalid dimension calculations. (#49848)
Nullable column row counts: Added Column.ValidCount() support so nullable columns can report the number of non-null rows separately from total row count. Struct-array columns return their total length. (#49848)

Milvus client/v2.6.5