test(stellar): cover normalizeStellarAddress edge cases

[webmirroring]

Summary

• add dedicated normalization coverage for whitespace trimming, case conversion, blank values, and non-string inputs
• assert that isValidStellarAddress accepts a lowercase, whitespace-padded valid G-address via normalization
• keep the change scoped to tests only

Closes #309.

Validation

• pnpm exec jest src/lib/__tests__/stellarAddress.test.ts --runInBand
• pnpm run lint
• pnpm test --runInBand
• ./node_modules/.bin/next build

Notes:

• Full Jest passed: 55 suites, 925 tests passing, 5 skipped.
• Build passed after using a pnpm hoist layout for the existing @jest/globals test-utils dependency in this local Codex environment.