S3 Select: optimize output (#8238)

Queue output items and reuse them.
Remove the unneeded type system in sql and just use the Go type system.

In best case this is more than an order of magnitude speedup:

```
BenchmarkSelectAll_1M-12    	       1	1841049400 ns/op	274299728 B/op	 4198522 allocs/op
BenchmarkSelectAll_1M-12    	      14	  84833400 ns/op	169228346 B/op	 3146541 allocs/op
```

pkg/s3select/csv/record.go

@@ -61,6 +61,33 @@ func (r *Record) Set(name string, value *sql.Value) error {
 	return nil
 }
 
+// Reset data in record.
+func (r *Record) Reset() {
+	if len(r.columnNames) > 0 {
+		r.columnNames = r.columnNames[:0]
+	}
+	if len(r.csvRecord) > 0 {
+		r.csvRecord = r.csvRecord[:0]
+	}
+	for k := range r.nameIndexMap {
+		delete(r.nameIndexMap, k)
+	}
+}
+
+// CopyFrom will copy all records from the incoming and append them to the existing records.
+// The source record must be of a similar type.
+// Note that the lookup index is not copied.
+func (r *Record) CopyFrom(record sql.Record) error {
+	other, ok := record.(*Record)
+	if !ok {
+		return fmt.Errorf("unexpected record type, expected %T, got %T", r, record)
+	}
+	//before := len(r.csvRecord)
+	r.columnNames = append(r.columnNames, other.columnNames...)
+	r.csvRecord = append(r.csvRecord, other.csvRecord...)
+	return nil
+}
+
 // WriteCSV - encodes to CSV data.
 func (r *Record) WriteCSV(writer io.Writer, fieldDelimiter rune) error {
 	w := csv.NewWriter(writer)