Add Stellar wallet address formatter tests

[kongwen686]

Summary

• add Stellar wallet address helpers for truncation, payment deep-link generation, and clipboard writes
• cover default truncation, short addresses, deep links, copy behavior, and invalid address handling

Verification

• node --test tests/walletAddress.test.mjs

Note: this local workspace links to an existing local node_modules directory containing the repository devDependency typescript to run the test. In a normal checkout, npm install/npm ci provides that dependency.

Closes #115

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