Complete NodeManager tests from decentralised nodes refactor

[tegefaulkes]

Specification

In a rush to get #618 complete, we didn't finish or convert all the tests we wanted. Theses need to be completed but can be done along side manual integration testing with the testnet.

#618 (comment) contains a description of the tests that still need to be done. The tests already exist within the test files as test.todo()s.

Additional context

• Related Decentralized Signalling #618
• Related Decentralized Signalling #618 (comment)

Tasks

• 1. findNode operations handle offline nodes/connection failures. Make sure that a single failing connection wont take up the full timeout of the process.
• 2. Network entry with syncNodeGraph, connects to 2 seed nodes and check we discover all active nodes in the network. Include active connection and direct connection links.
• 3. network entry with syncNodegraph handles offline nodes - just checking if we can handle offline nodes for the initial connections. The other connections are done by findNode. Also check that including our own NodeId in the initial connections list wont break.
• 4. refresh buckets - simple test, check that a scheduled refreshBucket triggers a findNode operation within that bucket. Not really worth the test.
• 5. checking NodeGraph updates when a connection is made.
• 6. test MDNS functionality. On that note, we need a way to disable it for testing so it doesn't break the findNode tests. Maybe just mock it out for most tests.
• 7. bunch of tests for adding new nodes and the background pinging tasks.
• 8. tests for signalling non-blocking and rate limiting logic.