fix(mobile): resolve validation test syntax errors and stellar service declarations

[NoobFaris]

Description

This PR resolves syntax errors in the validation tests and cleans up duplicate declarations in the Stellar service layer to ensure all test suites run cleanly.

Changes Included

• Fixed missing/unclosed block syntax errors in __tests__/validation.test.ts.
• Cleaned up duplicate declarations in src/services/stellar.ts.
• Ensured validation helpers (validateAddress, validateAmount, validateMemo) are properly tested with valid Stellar account key formats.

Testing

• Ran unit tests using pnpm test.
• All 16 test suites passed successfully (214 total unit tests).
  linked issues
  Closes Add mobile send form validation summary #141

[El-swaggerito]

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