feat(frontend): Create new variant type DIP721 for Custom tokens

[AntonioVentilii]

Motivation

We have a new variant DIP721 among the custom tokens, so we need to add it properly to the correct types.

Consequently, we need to adapt the mapping.

[Copilot]

Pull request overview

This PR adds support for the DIP721 variant to custom tokens in the frontend, including type definitions, utility mapping functions, service layer integration, and corresponding tests.

• Added Dip721SaveCustomToken type and Dip721 network key variant
• Implemented mapping function toDip721CustomToken to convert DIP721 tokens to backend format
• Extended hideTokenByKey to handle DIP721 tokens in the service layer

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/frontend/src/lib/types/custom-token.ts	Adds Dip721SaveCustomToken type and includes Dip721 variant in SaveCustomTokenWithKey union type
src/frontend/src/lib/utils/custom-token.utils.ts	Imports DIP721 type alias from backend declarations and implements toDip721CustomToken mapping function with network key handler
src/frontend/src/lib/services/save-custom-tokens.services.ts	Adds DIP721 store import, extends hideTokenByKey to handle DIP721, and includes TODO for missing loadCustomDip721Tokens
src/frontend/src/icp/stores/dip721-custom-tokens.store.ts	Creates new certified custom tokens store for DIP721 tokens
src/frontend/src/tests/lib/utils/custom-token.utils.spec.ts	Adds test case verifying correct type mapping for DIP721 network key
src/frontend/src/tests/lib/services/save-custom-tokens.services.spec.ts	Adds DIP721 mock token to test suite and verifies store reset behavior for disabled DIP721 tokens

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