eth: Refactor updateFilterMapsHeads to Use Timer Instead of time.After

[lukema95]

Issue Description

The updateFilterMapsHeads() function at eth/backend.go:511 uses time.After() inside a for-select loop. This creates a new timer object on every loop iteration. While Go 1.23+ can garbage collect these timers, this pattern is inefficient and goes against Go best practices for timer usage in loops.

Affected Code:

// File: eth/backend.go
// Line: 505-517

for {
    select {
    case ev := <-headEventCh:
        setHead(ev.Header)
    case blockProc := <-blockProcCh:
        s.filterMaps.SetBlockProcessing(blockProc)
    case <-time.After(time.Second * 10):  // ⚠️ INEFFICIENT: Creates new timer on each iteration
        setHead(s.blockchain.CurrentBlock())
    case ch := <-s.closeFilterMaps:
        close(ch)
        return
    }
}

Optimized code:

func (s *Ethereum) updateFilterMapsHeads() {
	// ... same setup ...

	// ✅ Refactor: Use timer with reset 
	timer := time.NewTimer(time.Second * 10)
	defer timer.Stop()

	for {
		select {
		case ev := <-headEventCh:
			setHead(ev.Header)
			timer.Reset(time.Second * 10)  // ✅ guarantees no stale values
			
		case blockProc := <-blockProcCh:
			s.filterMaps.SetBlockProcessing(blockProc)
			timer.Reset(time.Second * 10)  // ✅ guarantees no stale values
			
		case <-timer.C:
			setHead(s.blockchain.CurrentBlock())
			timer.Reset(time.Second * 10) // ✅ guarantees no stale values
			
		case ch := <-s.closeFilterMaps:
			close(ch)
			return
		}
	}
}

[jwasinger]

The current code is cleaner and the time interval is long enough that this can't effectively make a difference.