Code cleaning for URL construction

[anktd]

Changes

• Removed /api suffix from BASE_URL and BCH_BASE_URL constants
• Standardized API endpoint construction by explicitly adding /api prefix where needed
• Fixed transaction URL construction:
  • BTC: https://www.blockonomics.co/#/search?q={txid}&addr={address}
  • BCH: https://bch.blockonomics.co/api/tx?txid={txid}&addr={address}
• Updated all store-related API endpoints to use consistent /api/v2/stores pattern

Why

• Makes base URL constants more intuitive and less prone to bugs
• Ensures consistent API endpoint construction across the codebase
• Fixes BCH transaction URL format to match expected pattern
• Improves code maintainability by removing duplicate code