Integrate new p2panda high-level API

[adzialocha]

This patch integrates the new p2panda crate into the "backend" of Reflection.

p2panda is the new all-in-one high-level Node API which should make usage of p2panda features easier, removing a bunch of code in reflection-node which is now handled in p2panda directly, such as:

• Encoding / Decoding of operations and their message payloads
• Make sure changes to the append-only log are strictly serialized, to avoid breaking consistency / integrity of data due to race conditions
• Re-playing all operations on demand, this is required by Reflection to re-materialize all state for a document
• Manage header extensions to include log ids and prune flags
• Process local and remotely incoming operations ("ingest", "pruning")
• SQLite storage handling for logs and operations
• Mapping between logs and topics
• De-duplicate messages in ephemeral streams by adding timestamp
• Add public key / signatures to give provenance to ephemeral messages

Reflection Node

Some features implemented in reflection-node stay as they're adding functionality on top of p2panda. Some of them might be moved there as well in the future, such as:

• Author Presence: Indicate which authors have contributed to which topic and if they're currently online. Related issue: Presence extension to show who's online p2panda#1002
• Persisted Topics: Store to persist all previously used topics

Unfortunately we need to remove one feature for now which is to change "connection modes", causing the network to be disabled / enabled. reflection-node handled that well in the past by only disabling the networking layer while keeping the event processing layer intact. We will have to do something similar in p2panda to offer this feature as well since the new API surface will not allow such low-level access anymore. See related issue: p2panda/p2panda#1093

Breaking Changes

These changes introduce breaking changes to the core operation format (previous field was removed) and the header extensions changed which means that all previously created, persisted operations will not be compatible anymore.

THIS RESULTS IN LOOSING ALL PREVIOUSLY CREATED DOCUMENTS.

Since p2panda is not stable yet this might happen again in the near future, though this was the most important and largest update and we're much closer to a stable API and protocol now.

Final remarks

Some minor changes in reflection-doc where also necessary, I specifically decided to make p2panda-core a concrete dependency there since too much functionality is used to justify re-exports from reflection-node.

[jsparber]

Only had a quick look. Can you split code changes to sensible commits, e.g. creating the new database.rs file. Following the commit style https://handbook.gnome.org/development/commit-messages.html

[adzialocha]

Only had a quick look. Can you split code changes to sensible commits, e.g. creating the new database.rs file. Following the commit style https://handbook.gnome.org/development/commit-messages.html

Yeah, the commits are a bit unfortunate. Not sure I'm able to do this as this refactor kinda requires me to touch upon everything at the same time. I'll try to split them up a bit but no guarantee they'll compile in each patch.