feat: Make extension snapshotter interface safer to use (#11825)

* Make extension snapshotter interface safer to use

Closes: #11824
Solution:
- Use new methods `SnapshotExtension`/`RestoreExtension` to handle payload stream specifically.
- Improve unit tests.

* update changelog

* Update snapshots/types/util.go

* changelog

* go linter

* Update CHANGELOG.md

Co-authored-by: Aleksandr Bezobchuk <alexanderbez@users.noreply.github.com>

docs/architecture/adr-049-state-sync-hooks.md

@@ -3,10 +3,11 @@
 ## Changelog
 
 - Jan 19, 2022: Initial Draft
+- Apr 29, 2022: Safer extension snapshotter interface
 
 ## Status
 
-Draft, Under Implementation
+Implemented
 
 ## Abstract
 
@@ -107,11 +108,16 @@ func (m *Manager) RegisterExtensions(extensions ...types.ExtensionSnapshotter) e
 On top of the existing `Snapshotter` interface for the `multistore`, we add `ExtensionSnapshotter` interface for the extension snapshotters. Three more function signatures: `SnapshotFormat()`, `SupportedFormats()` and `SnapshotName()` are added to `ExtensionSnapshotter`.
 
 ```go
+// ExtensionPayloadReader read extension payloads,
+// it returns io.EOF when reached either end of stream or the extension boundaries.
+type ExtensionPayloadReader = func() ([]byte, error)
+
+// ExtensionPayloadWriter is a helper to write extension payloads to underlying stream.
+type ExtensionPayloadWriter = func([]byte) error
+
 // ExtensionSnapshotter is an extension Snapshotter that is appended to the snapshot stream.
 // ExtensionSnapshotter has an unique name and manages it's own internal formats.
 type ExtensionSnapshotter interface {
-	Snapshotter
-
 	// SnapshotName returns the name of snapshotter, it should be unique in the manager.
 	SnapshotName() string
 
@@ -120,6 +126,14 @@ type ExtensionSnapshotter interface {
 
 	// SupportedFormats returns a list of formats it can restore from.
 	SupportedFormats() []uint32
+
+	// SnapshotExtension writes extension payloads into the underlying protobuf stream.
+	SnapshotExtension(height uint64, payloadWriter ExtensionPayloadWriter) error
+
+	// RestoreExtension restores an extension state snapshot,
+	// the payload reader returns `io.EOF` when reached the extension boundaries.
+	RestoreExtension(height uint64, format uint32, payloadReader ExtensionPayloadReader) error
+
 }
 ```