Refactor: Improve API service architecture and add copyright notices

[carloskiron]

API Service Architecture Improvements & Copyright Notices

This PR improves the architecture of our API services and adds copyright notices to all source files. It contributes to issue #5 by implementing a more robust and maintainable API connection management system.

Changes

API Service Architecture

• Refactored ExplorerService to use a centralized Polkadot API connection
• Implemented proper dependency injection using tsyringe
• Created singleton pattern for API services to prevent multiple connections
• Added new services:
  • PolkadotApiService: Manages Polkadot.js API connections
  • ChainStateService: Handles chain state queries and subscriptions
  • ExplorerClient: Provides a global singleton access point

Code Organization

• Moved API-related code to dedicated service files
• Created interfaces for all services to improve maintainability
• Added proper type definitions
• Improved error handling and connection state management

Copyright Notices

• Added Apache 2.0 license copyright notice to all source files
• Standardized file headers across the codebase

Testing

The changes have been tested for:

• Proper API connection management
• Connection state handling
• Component re-rendering behavior

Breaking Changes

None. All existing functionality remains the same, but with improved internal architecture.

Next Steps

• Integration of timelock library (remove etf.js dependency)
• Unit tests for services

Contributes to #5