Merge bitcoin/bitcoin#29006: test: fix v2 transport intermittent test failure (#29002)

00e0658e77f66103ebdeb29def99dc9f937c049d test: fix v2 transport intermittent test failure (#29002) (Sebastian Falbesoner)

Pull request description:

  This PR improves the following fragile construct for detection of a new connection to the node under test in `p2p_v2_transport.py`:
  https://github.com/bitcoin/bitcoin/blob/6d5790956f45e3de5c6c4ee6fda21878b0d1287b/test/functional/p2p_v2_transport.py#L154-L156
  Only relying on the number of peers for that suffers from race conditions, as unrelated previous peers could disconnect at anytime in-between. In the test run in #29002, the following happens:

  - `getpeerinfo()` is called the first time -> assigned to `num_peers`
  - **previous peer disconnects**, the node's peer count is now `num_peers - 1` (in most test runs, this happens before the first getpeerinfo call)
  - new peer connects, the node's peer count is now `num_peers`
  - the condition that the node's peer count is `num_peers + 1` is never true, test fails

  Use the more robust approach of watching for an increased highest peer id instead (again using the `getpeerinfo` RPC call), with a newly introduced context manager method `TestNode.wait_for_new_peer()`. Note that for the opposite case of a disconnect, no new method is introduced; this is currently used only once in the test and is also simpler.

  Still happy to take suggestions for alternative solutions.

  Fixes #29002.

ACKs for top commit:
  kevkevinpal:
    Concept ACK [00e0658](https://github.com/bitcoin/bitcoin/pull/29006/commits/00e0658e77f66103ebdeb29def99dc9f937c049d)
  maflcko:
    Ok, lgtm ACK 00e0658e77f66103ebdeb29def99dc9f937c049d
  stratospher:
    ACK 00e0658.

Tree-SHA512: 0118b87f54ea5e6e080ff44f29d6af6674c757a588534b3add040da435f4359e71bf85bc0a5eb7170f99cc9956e1a03c35cce653d642d31eed41bbed1f94f44f

0 files changed, 0 insertions, 0 deletions