ATProto: implement sync v1.1 update

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https://github.com/bluesky-social/proposals/blob/main/0006-sync-iteration%2FREADME.md

Mainly new fields and blocks in #commits and ordering of blocks in CAR outputs. I don't think we currently have cases where we'd expect to enjoy the new #sync event, other than new account creation...? And the new com.atproto.sync.listReposByCollectionmethod and com.atproto.sync.getRepo subtree variant only seem like nice-to-haves...?

cc @bnewbold @anujahooja

[snarfed]

goat can now help verify this! https://bsky.app/profile/bnewbold.net/post/3lktb6hki2c2g

goat firehose --relay-host wss://pds.robocracy.org --verify-mst --verify-basic

[snarfed]

Test cases! https://github.com/bluesky-social/atproto-interop-tests/blob/main/firehose/commit-proof-fixtures.json