fix(node): preserve schemas for empty query results (#4423)

Empty local TypeScript queries returned a zero-row Arrow table with no
columns because `toArrow()` built the table solely from record batches.
Local streams can yield no batches, while remote streams often supply an
empty batch carrying the schema.

Expose the executed stream's schema through the native iterator and
decode it into an empty Arrow table when no batches arrive. This
preserves projected and search columns, types, nullability, and metadata
without executing another query. Document the empty-result behavior.

Validation:

- Eleven regression cases failed with the original `toArrow()`
implementation; all twelve now pass, including remote schema-only and
empty-batch responses.
- All 1,075 tests in the query, remote, Arrow, and table suites pass.
- Native build, TypeScript compilation, Rust formatting and Clippy (`-D
warnings`), TypeScript lint/formatting, and documentation generation
pass.

Fixes #4386

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generation=1 -->

Co-authored-by: Gatefixer <313497061+lancedb-gatefixer[bot]@users.noreply.github.com>

docs/src/js/classes/AutoQuery.md

@@ -417,6 +417,8 @@ Collect the results as an Arrow
 
 ArrowTable.
 
+Empty results retain the query's output schema.
+
 #### Inherited from
 
 `StandardQueryBase.toArrow`

docs/src/js/classes/Query.md

@@ -491,6 +491,8 @@ Collect the results as an Arrow
 
 ArrowTable.
 
+Empty results retain the query's output schema.
+
 #### Inherited from
 
 `StandardQueryBase.toArrow`

docs/src/js/classes/QueryBase.md

@@ -252,6 +252,8 @@ Collect the results as an Arrow
 
 ArrowTable.
 
+Empty results retain the query's output schema.
+
 ***
 
 ### withRowId()

docs/src/js/classes/TakeQuery.md

@@ -267,6 +267,8 @@ Collect the results as an Arrow
 
 ArrowTable.
 
+Empty results retain the query's output schema.
+
 #### Inherited from
 
 [`QueryBase`](QueryBase.md).[`toArrow`](QueryBase.md#toarrow)

docs/src/js/classes/VectorQuery.md

@@ -740,6 +740,8 @@ Collect the results as an Arrow
 
 ArrowTable.
 
+Empty results retain the query's output schema.
+
 #### Inherited from
 
 `StandardQueryBase.toArrow`