refactor(frontend): Expand logic of IC service loadNfts

[AntonioVentilii]

Motivation

We want to accomodate more standard in IC service loadNfts, so we refactor the logic to have a conditional check for the accepted standard.

[Copilot]

Pull request overview

This PR refactors the loadNfts function in the IC service to support multiple NFT token standards by introducing conditional logic to check token types. The refactoring sets up the infrastructure for accommodating additional standards beyond the currently supported EXT standard.

Key Changes:

• Introduced conditional token standard checking using isTokenExt type guard
• Added assertNever for exhaustiveness checking to ensure all token types are handled
• Renamed getTokensByOwner to getExtTokensByOwner for clarity

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/frontend/src/icp/services/nft.services.ts	Refactored loadNfts to use conditional logic for token standard checking, renamed imports for clarity, and added error handling for unsupported standards
src/frontend/src/tests/icp/services/nft.services.spec.ts	Updated test expectations to reflect renamed imports and added new test case to verify error handling for unsupported token standards

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