Add a unit test for the useNftMetadata fetch, error, and abort paths

[Baskarayelu]

Closes #983

Summary

• Add src/hooks/__tests__/useNftMetadata.test.ts with 6 focused test cases
• Covers the success (fetch) path with loading state transitions
• Covers HTTP error responses (404) with error message assertions
• Covers network errors surfaced as error strings
• Covers abort path via DOMException AbortError
• Covers the no-URL guard (does not call fetch, resets state)
• Covers re-fetch on subsequent refresh() calls

Test plan

• pnpm test src/hooks/__tests__/useNftMetadata.test.ts passes with all 6 tests green
• No regressions in other hook tests

🤖 Generated with Claude Code

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