Add multi table support to ResultsExplorer

[amontanez24]

Problem Description

I'd like to easily review the results of a multi-table benchmark run.
We want to expand the ResultsExplorer to work with other modalities (specifically multi-table).

Expected behavior

Add modality as a parameter to the ResultsExplorer.

from sdgym import ResultsExplorer

my_results_explorer = ResultsExplorer(
  path='s3://output_bucket',
  modality='multi_table'
)

This explorer should be able to navigate the new folder structure

output_destination/

|-- single-table 
    |-- SDGym_results_06_24_2025/
          |--- census_06_24_2025/
               |--- CTGANSynthesizer/  
                    |--- CTGANSynthesizer.pkl
                    |--- CTGANSynthesizer_synthetic_data.csv
                    |--- CTGANSynthesizer_benchmark_result.csv
               |--- TVAEynthesizer/  
                    |--- <artifacts>
          |--- expedia_hotel_logs_06_24_2025/
               |--- ...
          |--- meta.yaml
          |--- results.csv
     |--- SDGym_results_07_24_2025/
          |--- ...
|--- multi_table
     |--- SDGym_results_06_24_2025/
          |--- berka_06_24_2025/
               |--- HMASynthesizer/  
                    |--- HMASynthesizer.pkl
                    |--- HMASynthesizer_synthetic_data.zip
                    |--- HMASynthesizer_benchmark_result.csv
               |--- HSASynthesizer/  
                    |--- <artifacts>
          |--- synthea_06_24_2025/
               |--- ...
          |--- meta.yaml
          |--- results.csv
     |--- SDGym_results_07_24_2025/