[Chore] Add example for ensembling multiple logits during inference time

[sigridjineth]

Changes

• The PR introduces a example script that demonstrates the way to fuse dense, sparse and ColBERT-based scores using DBSF approaches.
• The example includes a detailed explanation of DBSF, which uses distribution-based normalization (mean ± 3*std) to make score ranges more stable before applying the final weighted ensemble. It helps users see how ColBERT scores, which may differ significantly in scale from Dense and Sparse scores, can be harmonized.