fix: copy push notification processor to transaction baseClient

- Copy pushProcessor from parent client to transaction in newTx()
- Ensure transactions inherit push notification processor from parent client
- Prevent nil pointer dereference in transaction contexts (Watch, Unwatch, etc.)
- Maintain consistent push notification behavior across all Redis operations

This fixes the panic that was occurring in transaction examples where the
transaction's baseClient had a nil pushProcessor field, causing segmentation
violations during transaction operations like Watch and Unwatch.

tx.go

@@ -27,6 +27,7 @@ func (c *Client) newTx() *Tx {
 			opt:           c.opt,
 			connPool:      pool.NewStickyConnPool(c.connPool),
 			hooksMixin:    c.hooksMixin.clone(),
+			pushProcessor: c.pushProcessor, // Copy push processor from parent client
 		},
 	}
 	tx.init()