Performance optimization: Consolidate Handler instances

[callebtc]

Description:
Multiple Handler instances are created across the app when a single shared instance could be used, leading to unnecessary resource usage.

Current Handler Usage:

• PosUiCoordinator.kt: mainHandler
• BalanceCheckActivity.kt: mainHandler
• Other activities likely creating their own handlers

Issues:

1. Unnecessary resource allocation
2. Multiple Handler instances for the same purpose
3. Potential handler leak if not cleaned up properly

Fix Instructions:
Create a shared Handler utility:

object HandlerUtils {
    val mainHandler: Handler by lazy { Handler(Looper.getMainLooper()) }
    
    fun postDelayed(action: () -> Unit, delayMillis: Long) {
        mainHandler.postDelayed(action, delayMillis)
    }
    
    fun post(action: () -> Unit) {
        mainHandler.post(action)
    }
    
    fun removeCallbacks(action: Runnable) {
        mainHandler.removeCallbacks(action)
    }
}

Usage:

// Replace individual Handler instances:
// private val mainHandler = Handler(Looper.getMainLooper())

// With shared utility:
HandlerUtils.postDelayed({ updateUI() }, 1000)

Benefits:

• Reduced memory usage
• Centralized handler management
• Easier cleanup and lifecycle management

Priority: Low - performance optimization