feat(monitoring): implement multi-signature monitoring and alert service

[rabsqueen]

📝 Summary

Implements the multi-signature monitoring module (#145) under src/modules/monitoring/multisig/. This module tracks wallet state changes, monitors approval progress, detects critical threshold and signer modifications, and dispatches security alerts via EventEmitter2.

Closes #145

🛠️ Changes Introduced

• src/modules/monitoring/multisig/types/multisig.types.ts:
  • Defined event types (SIGNER_ADDED, SIGNER_REMOVED, THRESHOLD_CHANGED, APPROVAL_SUBMITTED, EXECUTION_SUCCESS, EXECUTION_FAILED).
  • Added interfaces for MultisigAccountConfig, MultisigEvent, and MultisigAlert.
• src/modules/monitoring/multisig/multisig-monitoring.service.ts:
  • Added in-memory tracking for registered multisig wallet configurations.
  • Implemented state updates for signer changes and threshold modifications.
  • Added security alert detection and automatic emission of multisig.alert and multisig.activity events.
• src/modules/monitoring/multisig/multisig-monitoring.module.ts:
  • Registered MultisigMonitoringService and initialized EventEmitterModule.
• src/modules/monitoring/multisig/multisig-monitoring.service.spec.ts:
  • Implemented unit tests verifying wallet registration, threshold change detection, and alert emission.

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🧪 How to Test

1. Run the new unit tests:

   npm run test src/modules/monitoring/multisig/multisig-monitoring.service.spec.ts

[mijinummi]

LGTM! Well done @rabsqueen