feat: add use_index parameter to merge insert operations (#2674)

## Summary

Exposes `use_index` Merge Insert parameter, which was created upstream
in https://github.com/lancedb/lance/pull/4688.

## API Examples

### Python
```python
# Force table scan
table.merge_insert(["id"]) \
    .when_not_matched_insert_all() \
    .use_index(False) \
    .execute(data)
```

### Node.js/TypeScript
```typescript
// Force table scan  
await table.mergeInsert("id")
    .whenNotMatchedInsertAll()
    .useIndex(false)
    .execute(data);
```

### Rust
```rust
// Force table scan
let mut builder = table.merge_insert(&["id"]);
builder.when_not_matched_insert_all()
       .use_index(false);
builder.execute(data).await?;
```

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

nodejs/__test__/table.test.ts

@@ -487,6 +487,32 @@ describe("merge insert", () => {
         .execute(newData, { timeoutMs: 0 }),
     ).rejects.toThrow("merge insert timed out");
   });
+
+  test("useIndex", async () => {
+    const newData = [
+      { a: 2, b: "x" },
+      { a: 4, b: "z" },
+    ];
+
+    // Test with useIndex(true) - should work fine
+    const result1 = await table
+      .mergeInsert("a")
+      .whenNotMatchedInsertAll()
+      .useIndex(true)
+      .execute(newData);
+
+    expect(result1.numInsertedRows).toBe(1); // Only a=4 should be inserted
+
+    // Test with useIndex(false) - should also work fine
+    const newData2 = [{ a: 5, b: "w" }];
+    const result2 = await table
+      .mergeInsert("a")
+      .whenNotMatchedInsertAll()
+      .useIndex(false)
+      .execute(newData2);
+
+    expect(result2.numInsertedRows).toBe(1); // a=5 should be inserted
+  });
 });
 
 describe("When creating an index", () => {