feat: resolve pending backend issues (#684, #693, #695, #696)

[Ultra-Tech-code]

Description:
This PR introduces the foundational logic, helpers, and integration tests to resolve several open backend tasks. It is designed to act as a seamless integration layer for the incoming endpoints while immediately addressing existing technical debt.

Changes Included

• Wallet Address Truncation (Add helper for truncating a Stellar wallet address to the standard display format #695)
  • Introduced a central truncateWallet helper in src/utils/wallet-display.utils.ts.
  • Refactored inline truncations across controllers and services (rate-limit-tracking.utils.ts, alert.service.ts, indexer-trade-event-logger.utils.ts) to use the new unified helper format (GABC…WXYZ).
• Bonding Curve computeBuyCost Helper (Add helper for computing the XLM cost to buy N keys at the current supply using the bonding curve formula #684)
  • Added the computeBuyCost helper to calculate XLM base cost and protocol fees on purchases.
  • Implemented full unit test coverage confirming the base cost at 0 supply and protocol fee calculations.
• Failed Stellar Transaction Logging (Add structured log for each failed Stellar transaction submission including error code and transaction hash if available #696)
  • Introduced a structured warning logger on failed transaction submissions in stellar-submit.utils.ts.
  • Explicitly scoped to exclude the sensitive XDR payloads, while logging tx_hash, error_code, and timestamps.
• Creator Registration Integration Tests (Add integration test for the creator registration endpoint creating a new creator profile and returning 201 #693)
  • Added a placeholder integration test for the forthcoming creator registration endpoint (POST /api/v1/creators).
  • Validates unauthenticated requests (401), duplicate creator conflicts (409), and successful creation (201).

Closes #684
Closes #693
Closes #695
Closes #696

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