Activate crawler task based on a list of recent syncer obtain/extend lengths

[mpguerra]

Motivation

We want to control when we activate the network crawler task that will help us to populate the mempool. We want to be able to do this both for testing purposes as well as when zebra reaches the chain tip.

We also want to stop the mempool crawler if the syncer starts syncing large numbers of blocks again.

The crawler will receive a latest_sync_heights: watch::Receiver<Vec<usize>> to use to determine if it should be enabled or not, and the crawler should stop if that endpoint is closed.

The crawler will also receive a sender channel for transaction ID responses from peers. It should also stop if that channel is closed.

Designs

Mempool Design diagram

Related Work

#2592

[jvff]

The crawler will receive a latest_sync_heights: watch::Receiver<Vec<usize>> to use to determine if it should be enabled or not, and the crawler should stop if that endpoint is closed.

[jvff]

Closed by #2667.