docs: link guides to API and clarify dataset formats

[aroraanushri]

Closes #645

Hi @tejasstanley, following your suggestion in #596, this PR adds guide–API links and data-format documentation. It complements @sanket-jadhav-cse’s restructuring in #646.

Changes

• Added 17 guide-to-API links and 12 return links in source docstrings.
• Added COCO, YOLO, and Generic segmentation examples explaining annotations, file pairing, coordinates, and class IDs.
• Reused existing tutorials.
• Python changes affect docstrings only.

Validation

• Sphinx build passed with warnings treated as errors.
• Jekyll build and local preview completed.
• Verified API targets and generated return links.
• Checked the format examples against actual loader outputs using synthetic images.
• Sample image-segmentation evaluation completed on CPU for all 5 samples and produced metrics. Ontology-remapping and zero-denominator metric warnings were observed.
• Confirmed the patch combines with docs: renew PerceptionMetrics documentation #646 without conflicts using three-way application.