fix: resolve data race and leaked dialing counter in DialForOutboundPeers

[Sertug17]

Summary

Fixes the data race and permanent counter inflation reported in #491.

Changes in p2p/p2p.go

• Replaced plain int dialing variable with sync/atomic.Int64 to eliminate the data race between the initial DialPeers goroutines and the main loop
• Added defer dialing.Add(-1) in the initial goroutines so the counter correctly decrements when each DialWithBackoff call completes
• Updated all read/write sites to use .Add() and .Load()

Before

dialing := 0
go func() {
    dialing++ // unsynchronized, never decremented
    p.DialWithBackoff(peerAddress, true)
}()

After

var dialing atomic.Int64
go func() {
    dialing.Add(1)
    defer dialing.Add(-1) // correctly decrements on completion
    p.DialWithBackoff(peerAddress, true)
}()

Closes #491