ENH: implement edge and wrap modes for pad

[iamdhrv]

Closes #811

Summary

• Add array-API-compatible implementations for pad(..., mode="edge") and pad(..., mode="wrap").
• Keep the implementation backend-agnostic and preserve the existing constant-mode behavior.
• Extend delegated backend handling and add NumPy-oracle coverage for multidimensional, asymmetric, zero-width, singleton, and large padding cases.

Validation

• Test suite: 70 passed, 84 skipped for unavailable optional backends
• NumPy oracle comparisons passed
• Ruff passed
• mypy passed