d20a9fa13d tests: add tests for invalid P2P messages (James O'Beirne)
62f94d39f8 tests: add P2PConnection.send_raw_message (James O'Beirne)
5aa31f6ef2 tests: add utility to assert node memory usage hasn't increased (James O'Beirne)
Pull request description:
- Adds `p2p_invalid_messages.py`: tests based on behavior for dealing with invalid and malformed P2P messages. Includes a test verifying that we can't DoS a node by spamming it with large invalid messages.
- Adds `TestNode.assert_memory_usage_stable`: a context manager that allows us to ensure memory usage doesn't significantly increase on a node during some test.
- Adds `P2PConnection.send_raw_message`: which allows us to construct and send messages with tweaked headers.
Tree-SHA512: 720a4894c1e6d8f1551b2ae710e5b06c9e4f281524623957cb01599be9afea82671dc26d6152281de0acb87720f0c53b61e2b27d40434d30e525dd9e31fa671f