Add Soroban transaction status polling example (ISSUE-189)

[Olisachukwuma1]

Description

Implements a production-oriented Soroban transaction-status polling workflow as requested in ISSUE-189.

Changes

• src/examples/189-soroban-transaction-polling.ts: New example demonstrating:

  • Configurable polling interval with exponential backoff
  • Support for multiple transaction states (not found, pending, success, failed)
  • Timeout handling and graceful cancellation
  • Retry logic for temporary RPC failures
  • JSON output support
  • Transaction hash validation
  • Real-time polling progress display

• src/runner/catalog.ts: Registered example in the interactive runner

• src/validation/validation.config.json: Excluded from automated validation (requires live RPC)

• README.md: Updated with example documentation and usage instructions

Key Features

✅ Configurable polling interval and exponential backoff
✅ Support for all transaction states (not found, pending, success, failed)
✅ Timeout handling and graceful cancellation
✅ Temporary RPC failure retry with permanent error detection
✅ Transaction hash validation
✅ Real-time progress display with attempt numbers and elapsed time
✅ JSON output format
✅ Environment variable and CLI argument support

Usage

npm run run-example 189-soroban-transaction-polling

# With environment variables
SOROBAN_RPC_URL=https://... TRANSACTION_HASH=abc... npm run run-example 189-soroban-transaction-polling

Acceptance Criteria Met

• ✅ Runnable example polls until final state or timeout
• ✅ Transaction hashes are validated
• ✅ Pending transactions continue to be polled
• ✅ Successful transactions terminate polling
• ✅ Failed transactions terminate polling
• ✅ Not-found responses handled appropriately
• ✅ Exponential backoff configured correctly
• ✅ Maximum polling interval respected
• ✅ Overall timeout enforced
• ✅ Temporary RPC failures retried safely
• ✅ Permanent errors handled with useful message
• ✅ Graceful cancellation supported
• ✅ Polling progress displayed
• ✅ JSON output works
• ✅ Registered in interactive runner
• ✅ Documented in README

Closes #249

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