Feature/omics layers

[DanielGarbozo]

Summary

This PR introduces a new omics-layers feature set to OmicsKit, adding survival analysis utilities,
multi-omics visualization functions, and genomic track support, along with full documentation and tests
for each addition.

New Functions

• get_cox() + nice_forest() – Cox proportional hazards regression and forest plot visualization for survival analysis.
• get_glm() + nice_ROC() – Generalized linear model fitting with ROC curve visualization for binary outcome analysis.
• trend_filter() / updated detect_filter() – Trend-based filtering utilities for omics feature selection.
• nice_KM() – Kaplan-Meier survival curve visualization (tests added).
• nice_circos() – Circos plot function for multi-omics circular visualization.
• nice_GenomeTrack() – Genome track visualization with Ensembl-driven annotations and local annotation support.
• Concordance functions – C-index and concordance metrics for model evaluation.

Fixes & Improvements

• Offline-safe tests and local annotation fallback for nice_GenomeTrack().
• Mocked biomaRt calls in get_annotations() tests for CI compatibility.
• Stable Ensembl host pinned in get_annotation tests to avoid version drift.

Chores

• Synced branch with upstream/dev via merge commit.