feat(keeper): implement retry logic with exponential backoff for failed submissions

[ACodehunter]

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