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Add Apache Arrow result streaming to DuckDBCommand (#334)

* Add Apache Arrow result streaming to DuckDBCommand

Adds a managed Apache Arrow read surface built on DuckDB's current Arrow C Data
Interface (duckdb_to_arrow_schema / duckdb_data_chunk_to_arrow), addressing #26.

- Bindings: duckdb_result_get_arrow_options, duckdb_to_arrow_schema,
  duckdb_data_chunk_to_arrow, error-data helpers, and a DuckDBArrowOptions safe handle.
- Data: DuckDBArrowArrayStream (IArrowArrayStream) that builds the schema once and
  converts each data chunk into an Arrow RecordBatch via Apache.Arrow's C importers.
- DuckDBCommand.ExecuteArrowStream() and ExecuteArrowBatchesAsync() public APIs.
- Apache.Arrow dependency added to DuckDB.NET.Data only.
- Tests covering schema, scalar values, nulls, multi-chunk streaming, and the stream API.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Honor UseStreamingMode in Arrow APIs and fix result stream cleanup

Pass UseStreamingMode through ExecuteArrowStream and fetch chunks via the
streaming or materialized path accordingly. Dispose Arrow options and close
the result if schema building fails in the stream constructor. Add tests for
streaming mode, cancellation, and dispose semantics.

* Refactor Arrow error handling to typed DuckDBErrorData handle

- Add DuckDBErrorData SafeHandle wrapping duckdb_error_data
- Move error-data P/Invokes to NativeMethods.ErrorData
- Retype duckdb_to_arrow_schema/data_chunk_to_arrow returns to DuckDBErrorData
- Add reusable ThrowOnError extension throwing DuckDBException
- Make DuckDBArrowArrayStream internal

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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