Fix Windows non-blocking I/O for CopyFrom

Created based on discussion here: https://github.com/jackc/pgx/pull/1525#pullrequestreview-1344511991

Fixes https://github.com/jackc/pgx/issues/1552

copy_from.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"github.com/jackc/pgx/v5/internal/nbconn"
 	"io"
 
 	"github.com/jackc/pgx/v5/internal/pgio"
@@ -134,6 +135,17 @@ func (ct *copyFrom) run(ctx context.Context) (int64, error) {
 	r, w := io.Pipe()
 	doneChan := make(chan struct{})
 
+	if realNbConn, ok := ct.conn.pgConn.Conn().(*nbconn.NetConn); ok {
+		if err := realNbConn.SetBlockingMode(false); err != nil {
+			return 0, fmt.Errorf("cannot set socket non-blocking mode: %w", err)
+		}
+
+		defer func() {
+			// TODO: Deal with it
+			_ = realNbConn.SetBlockingMode(true)
+		}()
+	}
+
 	go func() {
 		defer close(doneChan)