Feature/stellar interceptor system

[tech-adrian]

This PR implements a comprehensive interceptor system for the NFTopia NestJS backend to handle Stellar-specific request and response transformations, Soroban contract error handling, transaction logging, and configurable timeouts.

Closes #67

Changes Proposed

• Stellar System Configuration: Added src/config/stellar.config.ts to manage environment-specific variables like the RPC URL, network passphrase, and granular timeout configurations for simulations vs. submissions.
• Custom Error Taxonomy: Introduced domain-specific Stellar errors in src/common/errors/stellar.errors.ts (SorobanRpcError, TransactionFailedError, InsufficientBalanceError, InvalidSignatureError, ContractError).
• Response Standardization: Added StellarResponseInterceptor to wrap outgoing DTOs in a consistent { data, meta } format, automatically injecting the network context, timestamp, and optional transaction markers.
• Transaction Logging: Implemented StellarLoggingInterceptor utilizing Nest's logging utilities to trace RPC timings, Soroban contract calls, and general Stellar endpoint usage.
• Error classification & Masking: Implemented StellarErrorInterceptor to catch our custom StellarError types, map them to standard HTTP exceptions (like 502 Bad Gateway or 400 Bad Request), and automatically redact sensitive secret seeds (starting with S) from error traces.
• Robust Timeouts: Added StellarTimeoutInterceptor relying on RxJS timeout operators to cancel hanging Soroban streams and simulations based on configurable thresholds.
• Data Transformation: Added StellarTransformInterceptor to unwrap Horizon pagination cursors correctly and normalize raw Stroops into XLM string decimal formats.
• Application Wiring: Refactored src/nft/soroban.service.ts to throw the new custom exceptions and globally registered all interceptors and configs within src/main.ts and src/app.module.ts.

Acceptance Criteria Evaluated

• Stellar response standardization interceptor created.
• Stellar transaction logging interceptor implemented.
• Global error handling interceptor created with error classifying.
• Stellar transaction timeout interceptor added.
• Stellar account data transformation and pagination unwrapping handled.
• Timeouts and environments configurable via stellar.config.ts.
• Secret seeds and sensitive data obfuscated from error messages.

How to Test

1. Pull the branch feature/stellar-interceptor-system.
2. Ensure you have your SOROBAN_RPC_URL and STELLAR_NETWORK environment variables set.
3. Observe standard terminal output for timing metrics when hitting /api/v1/nft routes.
4. Verify HTTP error statuses when triggering invalid Soroban transactions (mockable via service throws).

[tech-adrian]

@Oluwaseyi89 please review

[tech-adrian]

@Oluwaseyi89 please review and merge

[Oluwaseyi89]

@Caxton22 resolve the linting errors.