reduce recursion level of unparser part

### Is your feature request related to a problem or challenge?

Related to https://github.com/apache/datafusion/pull/19109#discussion_r2670731564

### Describe the solution you'd like

Unparser's deep recursion can overflow the stack easily, especially for complex analytical queries like those from tpc-h

### Describe alternatives you've considered

Convert the current implementation to an iterative flavor

### Additional context

_No response_