Add Asset delete/restore methods

[evanvolgas]

Summary

The SDK's Assets resource is missing delete and restore operations that exist in the core API.

Core API endpoints to support

• DELETE /assets/{id} - Soft delete asset
• POST /assets/{id}/restore - Restore deleted asset

Methods to add

class AssetsResource:
    def delete(self, asset_id: UUID) -> None:
        """Soft delete an asset."""
        
    def restore(self, asset_id: UUID) -> Asset:
        """Restore a soft-deleted asset."""

Use case

Asset lifecycle management - removing deprecated assets while maintaining audit history.