fuzz-tests: add a test for handle_peer_error_or_warning()

[Chand-ra]

handle_peer_error_or_warning() in common/read_peer_message is responsible for parsing any incoming error or warning messages as defined in BOLT #1. Add a test for it.

Checklist

Before submitting the PR, ensure the following tasks are completed. If an item is not applicable to your PR, please mark it as checked:

• The changelog has been updated in the relevant commit(s) according to the guidelines.
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.

[Chand-ra]

@morehouse , I think this test has exposed a bug, although I'm not 100% confident.

We're injecting the fuzzer input as msg to handle_peer_error_or_warning(struct per_peer_state *pps, const u8 *msg). I've looked into this function's callers and I'm pretty sure msg is derived from the wire in most of them. I set up a similar test for the ping-pong message handler:

void run(const uint8_t *data, size_t size)
{
    u8 *pong;
    u8 *buf = tal_dup_arr(tmpctx, u8, data, size, 0);
    check_ping_make_pong(tmpctx, buf, &pong);

    clean_tmpctx();
}

and that works without any breakage.