Add integration wrapper for the U-method package

[YanuvS]

This PR introduces a SeuratWrappers interface for the U-method (FindUniqueMarkers.Seurat).

The U-method is a fast, probability-based framework optimized for robust cell-type gene identification via maximum-outside cluster contrast evaluation, operating directly on expression probabilities without the need for downstream normalization, batch correction, or smoothing.

Designed to serve as a complementary feature to standard magnitude-based differential expression (DE) methods, the algorithm ranks genes based on the stability of their expression pattern, identifying high-contrast markers that are consistently not expressed across the background populations.

This wrapper accepts standard Seurat objects, performs early-stage cluster size and factor verification checks, and seamlessly feeds results back into the ecosystem.

Reference preprint: Stein et al. (2026). "The U-method: Leveraging expression probability for robust biological marker detection." bioRxiv.