cmd/devp2p/internal/ethtest: add correct chain files and improve test output (#21782)

This PR replaces the old test genesis.json and chain.rlp files in the testdata
directory for the eth protocol test suite, and also adds documentation for
running the eth test suite locally.

It also improves the test output text and adds more timeouts.

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

cmd/devp2p/internal/ethtest/chain_test.go

@@ -73,7 +73,7 @@ func TestEthProtocolNegotiation(t *testing.T) {
 // TestChain_GetHeaders tests whether the test suite can correctly
 // respond to a GetBlockHeaders request from a node.
 func TestChain_GetHeaders(t *testing.T) {
-	chainFile, err := filepath.Abs("./testdata/chain.rlp.gz")
+	chainFile, err := filepath.Abs("./testdata/fullchain.rlp.gz")
 	if err != nil {
 		t.Fatal(err)
 	}