* Somewhat complete the implementation of Kademlia records. This commit relates to [libp2p-146] and [libp2p-1089]. * All records expire (by default, configurable). * Provider records are also stored in the RecordStore, and the RecordStore API extended. * Background jobs for periodic (re-)replication and (re-)publication of records. Regular (value-)records are subject to re-replication and re-publication as per standard Kademlia. Provider records are only subject to re-publication. * For standard Kademlia value lookups (quorum = 1), the record is cached at the closest peer to the key that did not return the value, as per standard Kademlia. * Expiration times of regular (value-)records is computed exponentially inversely proportional to the number of nodes between the local node and the closest node known to the key (beyond the k closest), as per standard Kademlia. The protobuf messages are extended with two fields: `ttl` and `publisher` in order to implement the different semantics of re-replication (by any of the k closest peers to the key, not affecting expiry) and re-publication (by the original publisher, resetting the expiry). This is not done yet in other libp2p Kademlia implementations, see e.g. [libp2p-go-323]. The new protobuf fields have been given somewhat unique identifiers to prevent future collision. Similarly, periodic re-publication of provider records does not seem to be done yet in other implementations, see e.g. [libp2p-js-98]. [libp2p-146]: #146 [libp2p-1089]: #1089 [libp2p-go-323]: libp2p/go-libp2p-kad-dht#323 [libp2p-js-98]: libp2p/js-libp2p-kad-dht#98 * Tweak kad-ipfs example. * Add missing files. * Ensure new delays are polled immediately. To ensure task notification, since `NotReady` is returned right after. * Fix ipfs-kad example and use wasm_timer. * Small cleanup. * Incorporate some feedback. * Adjustments after rebase. * Distinguish events further. In order for a user to easily distinguish the result of e.g. a `put_record` operation from the result of a later republication, different event constructors are used. Furthermore, for now, re-replication and "caching" of records (at the closest peer to the key that did not return a value during a successful lookup) do not yield events for now as they are less interesting. * Speed up tests for CI. * Small refinements and more documentation. * Guard a node against overriding records for which it considers itself to be the publisher. * Document the jobs module more extensively. * More inline docs around removal of "unreachable" addresses. * Remove wildcard re-exports. * Use NonZeroUsize for the constants. * Re-add method lost on merge. * Add missing 'pub'. * Further increase the timeout in the ipfs-kad example. * Readd log dependency to libp2p-kad. * Simplify RecordStore API slightly. * Some more commentary. * Change Addresses::remove to return Result<(),()>. Change the semantics of `Addresses::remove` so that the error case is unambiguous, instead of the success case. Use the `Result` for clearer semantics to that effect. * Add some documentation to .