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>

cmd/utils/flags.go

@@ -267,7 +267,7 @@ var (
 		Value:    2048,
 		Category: flags.EthCategory,
 	}
-	OverrideShanghai = &flags.BigFlag{
+	OverrideShanghai = &cli.Uint64Flag{
 		Name:     "override.shanghai",
 		Usage:    "Manually specify the Shanghai fork timestamp, overriding the bundled setting",
 		Category: flags.EthCategory,