cmd/devp2p: verify client doesn't disconnect when non-existent block is requested

[1033309821]

We added tests for GetBlockHeaders data similar to what we did in the D2PFuzz project to the devp2p suite.

[1033309821]

#31471

[jwasinger]

The tests should be predictable. These currently use randomly-generated values, meaning that if a failure pops up, it cannot be reproduced in a subsequent run.

Also, IMO test cases should have a focused scope and aim to capture some specific behavior (like reproducing a specific bug/client-mismatch that was found), instead of be a "catch-all".

[1033309821]

Dear jwasinger,
Thank you for your advice and guidance. This test checks if geth will disconnect from a peer that sends an incorrect GetBlockHeaders packet. In our tests, we found that geth and erigon clients will not disconnect, while reth, besu, and nethermind will disconnect from the peer after receiving an incorrect GetBlockHeaders packet.

[lightclient]

I inverted the test to fail if the client disconnects. The devp2p protocol does not specify a client should disconnect when it receives a valid request for a non-existent header.