Arroba

Notable changes

* Bug fix: base32-encode TIDs in record keys, `at://` URIs, commit `rev`s, etc. Before, we were using the integer UNIX timestamp directly, which happened to be the same 13 character length. Oops.
* Switch from `BGS_HOST` environment variable to `RELAY_HOST`. `BGS_HOST` is still supported for backward compatibility.
* `datastore_storage`:
* Bug fix for `DatastoreStorage.last_seq`, handle new NSID.
* Add new `AtpRemoteBlob` class for storing "remote" blobs, available at public HTTP URLs, that we don't store ourselves.
* `did`:
* `create_plc`: strip padding from genesis operation signature (for [did-method-plc54](https://github.com/did-method-plc/did-method-plc/pull/54), [atproto#1839](https://github.com/bluesky-social/atproto/pull/1839)).
* `resolve_handle`: return None on bad domain, eg `.foo.com`.
* `resolve_handle` bug fix: handle `charset` specifier in HTTPS method response `Content-Type`.
* `util`:
* `new_key`: add `seed` kwarg to allow deterministic key generation.
* `xrpc_repo`:
* `getRecord`: try to load record locally first; if not available, forward to AppView.
* `xrpc_sync`:
* Implement `getBlob`, right now only based on "remote" blobs stored in `AtpRemoteBlob`s in datastore storage.

Notable changes

* Migrate to [ATProto repo v3](https://atproto.com/blog/repo-sync-update). Specifically, the existing `subscribeRepos` sequence number is reused as the new `rev` field in commits. ([Discussion.](https://github.com/bluesky-social/atproto/discussions/1607)).
* Add new `did` module with utilities to create and resolve `did:plc`s and resolve `did:web`s.
* Add new `util.service_jwt` function that generates [ATProto inter-service JWTs](https://atproto.com/specs/xrpc#inter-service-authentication-temporary-specification).
* `Repo`:
* Add new `signing_key`/`rotation_key` attributes. Generate store, and load both in `datastore_storage`.
* Remove `format_init_commit`, migrate existing calls to `format_commit`.
* `Storage`:
* Rename `read_from_seq` => `read_blocks_by_seq` (and in `MemoryStorage` and `DatastoreStorage`), add new `read_commits_by_seq` method.
* Merge `load_repo` `did`/`handle` kwargs into `did_or_handle`.
* XRPCs:
* Make `subscribeRepos` check storage for all new commits every time it wakes up.
* As part of this, replace `xrpc_sync.enqueue_commit` with new `send_new_commits` function that takes no parameters.
* Drop bundled `app.bsky`/`com.atproto` lexicons, use [lexrpc](https://lexrpc.readthedocs.io/)'s instead.

Big milestone: arroba is successfully federating with the [ATProto sandbox](https://atproto.com/blog/federation-developer-sandbox)! See [app.py](https://github.com/snarfed/arroba/blob/main/app.py) for the minimal demo code needed to wrap arroba in a fully functional PDS.

* Add Google Cloud Datastore implementation of repo storage.
* Implement `com.atproto` XRPC methods needed to federate with sandbox, including most of `repo` and `sync`.
* Notably, includes `subscribeRepos` server side over websocket.
* ...and much more.

Implement repo and commit chain in new Repo class, including pluggable storage. This completes the first pass at all PDS data structures. Next release will include initial implementations of the `com.atproto.sync.*` XRPC methods.

Initial release! Still very in progress. MST, Walker, and Diff classes are mostly complete and working. Repo, commits, and sync XRPC methods are coming soon.