opt: optimize cluster identification

[tediou5]

Second attempt to close #2900

The first commit is meaningless; it simply renames cache_id to piece_cache_id

For the cache, everything is straightforward; it's just a matter of recording the corresponding relationships in the controller. However, things are a litter bit more complicated for the farmer. First, we check the identify message to see if the farmer is newly discovered and whether the fingerprint has changed. Based on the results, we decide whether to use the stream to fetch details.

The final commit is to ensure compatibility with previous approaches.

(I’m really sorry, actually, I finished it a long time ago, but I forgot about it and left it in a corner.)

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[tediou5]

@nazar-pc additionally, during my actual development, this part of the code is not easy to test, and some scenarios are hard to cover(like farm FingerprintUpdated). At the very least, I need to start 3 components: nats, controller, and farmer/cache to do so. I was thinking maybe I could first submit a PR to extract the update logic for caches and farms and cover enough test cases?