Add GET /account/:id/claimable-balances endpoint

[Bhenzdizma]

1. Error Handler (/src/utils/errors.js): Added makeClaimableBalanceNotFoundError() for handling claimable balance not found scenarios.
2. GET /account/:id/claimable-balances (/src/routes/account.js): Returns all claimable balances where the account is a claimant. Supports pagination with limit and cursor query parameters.
3. GET /account/:id/data (/src/routes/account.js): Returns all data entries stored on the account, formatted as key-value pairs.
   4 Add validation for claimable balance ID format

Both endpoints:

• Validate the account ID
• Handle 404 errors gracefully via the existing handleAccountNotFound utility
• Follow the existing response format using the success() utility

closes #375
closes #376
closes #370
closes #369

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[Sulex45]

Kindly resolve conflicts