* Rewrite some state cache docs to clarify
* Add a zebra_network::Config.cache_dir for peer address caches
* Add new config test files and fix config test failure message
* Create some zebra-chain and zebra-network convenience functions
* Add methods for reading and writing the peer address cache
* Add cached disk peers to the initial peers list
* Add metrics and logging for loading and storing the peer cache
* Replace log of useless redacted peer IP addresses
* Limit the peer cache minimum and maximum size, don't write empty caches
* Add a cacheable_peers() method to the address book
* Add a peer disk cache updater task to the peer set tasks
* Document that the peer cache is shared by multiple instances unless configured otherwise
* Disable peer cache read/write in disconnected tests
* Make initial peer cache updater sleep shorter for tests
* Add unit tests for reading and writing the peer cache
* Update the task list in the start command docs
* Modify the existing persistent acceptance test to check for peer caches
* Update the peer cache directory when writing test configs
* Add a CacheDir type so the default config can be enabled, but tests can disable it
* Update tests to use the CacheDir config type
* Rename some CacheDir internals
* Add config file test cases for each kind of CacheDir config
* Panic if the config contains invalid socket addresses, rather than continuing
* Add a network directory to state cache directory contents tests
* Add new network.cache_dir config to the config parsing tests
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