feat(transactions): implement monitorTransaction polling loop

[ExcelDsigN-tech]

[Feat] Implement monitorTransaction polling loop for transaction builders (Closes #121)

Overview

This PR introduces the monitorTransaction utility within the SDK, providing a robust mechanism for polling the Horizon network until a transaction reaches a terminal state (confirmed, failed, or timed out). This is a core component of the Transaction Builders epic, ensuring reliable feedback for asynchronous Stellar operations.

Feature Summary

• Polling Engine: Implemented monitorTransaction with configurable maxAttempts and intervalMs to track transaction lifecycle.
• Smart Backoff: Added exponential backoff logic that triggers after 5 consecutive "not found" responses to optimize network overhead.
• Status Resolution: Calculates ledger confirmations (currentLedger - txLedger) and returns standardized TransactionStatus objects.
• Error Handling: Introduced MonitorTimeoutError for exceeded attempts and explicit failure states for rejected transactions.

Technical Implementation

The implementation centers on a polling loop that leverages a new internal fetchTransactionOnce helper. The loop manages state transition from "not found" to "terminal" while respecting the exponential backoff window. It is designed to be CI-friendly and integrates directly into the package entrypoint for consumer accessibility.

Test Coverage

• Resilience Testing: Verified successful resolution on the 3rd attempt after initial "not found" states.
• Exception Handling: Confirmed MonitorTimeoutError triggers correctly using Jest fake timers.
• Logic Validation: Validated confirmation count math and failure state mapping for rejected transactions.

Checklists

• Implement monitorTransaction with configurable retry options
• Add fetchTransactionOnce for atomic Horizon lookups
• Integrate exponential backoff for persistent "not found" scenarios
• Export transaction monitoring utilities from the SDK entrypoint
• Pass lint, type-check, and unit-test suites

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[amina69]

@ExcelDsigN-tech you are making pr to the wrong branch, read the conributing.md