build: add imports for go generate tools (#24682)

This adds a tools.go file to import all command packages used for
go:generate. Doing so makes it possible to execute go-based code
generators using 'go run', locking in the tool version using go.mod.

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

eth/ethconfig/config.go

@@ -116,7 +116,7 @@ func init() {
 	}
 }
 
-//go:generate gencodec -type Config -formats toml -out gen_config.go
+//go:generate go run github.com/fjl/gencodec -type Config -formats toml -out gen_config.go
 
 // Config contains configuration options for of the ETH and LES protocols.
 type Config struct {