refactor: Decouple client.DB from net (#2768)

## Relevant issue(s)

Resolves #2767 

## Description

This PR make the `net` package no longer dependent on `client.DB`.
Instead, on creation, the peer takes in a rootstore, a blockstore and an
event bus.

The p2p collections and replicators have been moved to `db`. Most of the
code is reused but it now makes use of the event bus to update the
peer's related state (pubsub topics and peer connections).

client/db.go

@@ -42,13 +42,13 @@ type DB interface {
 	// can safely operate on it concurrently.
 	NewConcurrentTxn(context.Context, bool) (datastore.Txn, error)
 
-	// Root returns the underlying root store, within which all data managed by DefraDB is held.
-	Root() datastore.RootStore
+	// Rootstore returns the underlying root store, within which all data managed by DefraDB is held.
+	Rootstore() datastore.Rootstore
 
 	// Blockstore returns the blockstore, within which all blocks (commits) managed by DefraDB are held.
 	//
 	// It sits within the rootstore returned by [Root].
-	Blockstore() datastore.DAGStore
+	Blockstore() datastore.Blockstore
 
 	// Peerstore returns the peerstore where known host information is stored.
 	//
@@ -106,6 +106,11 @@ type Store interface {
 	// Backup holds the backup related methods that must be implemented by the database.
 	Backup
 
+	// P2P contains functions related to the P2P system.
+	//
+	// These functions are only useful if there is a configured network peer.
+	P2P
+
 	// AddSchema takes the provided GQL schema in SDL format, and applies it to the [Store],
 	// creating the necessary collections, request types, etc.
 	//

client/errors.go

@@ -56,6 +56,7 @@ var (
 	ErrCanNotNormalizeValue                = errors.New(errCanNotNormalizeValue)
 	ErrCanNotTurnNormalValueIntoArray      = errors.New(errCanNotTurnNormalValueIntoArray)
 	ErrCanNotMakeNormalNilFromFieldKind    = errors.New(errCanNotMakeNormalNilFromFieldKind)
+	ErrCollectionNotFound                  = errors.New(errCollectionNotFound)
 )
 
 // NewErrFieldNotExist returns an error indicating that the given field does not exist.