feat: add ISSUE-190 Soroban transaction event monitor example

[Olisachukwuma1]

• Add src/examples/190-soroban-transaction-event-monitor.ts
  • Validates transaction hash (64 hex chars)
  • Polls until terminal state with configurable interval/maxInterval/timeout
  • Retries on transient RPC failures without terminating
  • Retrieves contract events and diagnostic events by ledger window
  • Decodes ScVal topics and data with formatNativeValue (JSON-safe)
  • Groups events by contract and event type/name
  • Preserves raw XDR alongside decoded values
  • Handles no-event, failed tx, timeout, and unsupported ScVal cases
  • Supports JSON output via params.json or JSON_OUTPUT env var
• Add tests/soroban-transaction-event-monitor.test.ts
  • Covers hash validation, polling, timeout, transient errors
  • Covers event parsing, topic/value decoding, grouping
  • Covers empty events, failed tx, JSON output
  • Covers runner registration and README documentation
• Register example in src/runner/catalog.ts with rpcUrl/txHash prompts
• Add entry to README example catalog

Summary

Describe the changes introduced by this Pull Request.

Related Issue

Closes #250

Type of Change

• 🚀 New example script added
• 🐛 Bug fix (fixes an execution error in an example)
• 📝 Documentation update (updates inline commentary or README)
• 🧪 Test improvement

Changes Made

• List changes made
• Note any testnet addresses or networks tested against

Testing

• The example runs successfully on Testnet (npm run run-example <name>)
• Linter check passes (npm run lint)
• Type check passes (npm run typecheck)

CLI Output

Paste successful execution logs from your terminal here.

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