all: make timestamp-based fork checks based on uint64 (#26474)

This PR changes the API so that uint64 is used for fork timestamps.
It's a good choice because types.Header also uses uint64 for time.

Co-authored-by: Felix Lange <fjl@twurst.com>

light/txpool.go

@@ -318,7 +318,7 @@ func (pool *TxPool) setNewHead(head *types.Header) {
 	next := new(big.Int).Add(head.Number, big.NewInt(1))
 	pool.istanbul = pool.config.IsIstanbul(next)
 	pool.eip2718 = pool.config.IsBerlin(next)
-	pool.shanghai = pool.config.IsShanghai(big.NewInt(time.Now().Unix()))
+	pool.shanghai = pool.config.IsShanghai(uint64(time.Now().Unix()))
 }
 
 // Stop stops the light transaction pool