…ed submissions

Implements a fault-tolerant retry mechanism for transaction submissions that
handles transient network failures, RPC timeouts, and fee-related rejections
without causing duplicate execution or infinite loops.

Features:
- Generic withRetry() higher-order async wrapper with configurable options
- Exponential backoff with jitter: baseDelay * 2^attempt + random(0, baseDelay)
- Error classification into retryable, non-retryable, and duplicate categories
- DUPLICATE_TRANSACTION responses treated as success (no retry)
- Comprehensive error code support for Soroban RPC responses
- Retry count tracking and inclusion in execution logs
- MAX_RETRIES_EXCEEDED warning event emission
- Environment variable configuration (MAX_RETRIES, RETRY_BASE_DELAY_MS, MAX_RETRY_DELAY_MS)

Error Classifications:
- Retryable: TIMEOUT, NETWORK_ERROR, RATE_LIMITED, SERVER_ERROR, etc.
- Non-retryable: INVALID_ARGS, INSUFFICIENT_GAS, CONTRACT_PANIC, TX_BAD_AUTH, etc.
- Duplicate: DUPLICATE_TRANSACTION, TX_ALREADY_IN_LEDGER

Testing:
- Unit tests covering success on 2nd attempt
- Non-retryable error bail scenarios
- Max retries exceeded handling
- Duplicate transaction detection
- Exponential backoff with jitter verification
- Network error detection

Closes SoroLabs#37