Add tests for `DetectionMetricsFactory`

[dpascualhe]

Our current tests provide good coverage for SegmentationMetricsFactory and other modules in utils, but there are no unit tests for the DetectionMetricsFactory class and standalone functions in detection_metrics.py.

Deliverables: a new test_detection_metrics.py with unit tests for the detection_metrics module. Renaming of the current test_metrics.py to test_segmentation_metrics.py to avoid confusion.

[iocalangiu]

Hi, I am working on the tests and will update in 2h how far I got.

[iocalangiu]

Hi! So far I have implemented the following unit tests:

• test_match_predictions_logic: Verifies TP/FP assignment logic.
• test_compute_metrics: Validates Precision/Recall/AP and double-detection penalties.
• test_compute_iou_matrix_basic: Checks the geometric IoU matrix calculation.
• test_compute_coco_map_sensitivity: Validates mAP across thresholds.
• test_compute_coco_map_perfect_match: Test that a perfect overlap results in a 1.0 COCO mAP.

Working on tests for:
get_overall_precision_recall_curve, compute_auc_pr, get_metrics_dataframe, compute_ap.

I will open the PR as soon as I'm done with that.