fix: detect identity key changes and reset sessions (align with WA Web) (#2307)

* feat(signal): add RetryReason enum and MAC error-based session recreation

* feat(signal): add identity change detection with automatic session clearing

* fix(signal): integrate identity change detection with pkmsg decryption

This completes the identity change detection implementation by actually
calling saveIdentity() during pkmsg decryption, which is CRITICAL for
the feature to work.

Changes:
- Add extractIdentityFromPkmsg() function that parses PreKeyWhisperMessage
  protobuf to extract sender's identity key (33 bytes)
- Call saveIdentity() BEFORE decryption in decryptMessage() for pkmsg type
- Log when identity change is detected

Flow:
1. Receive pkmsg from sender
2. Extract identity key from PreKeyWhisperMessage protobuf
3. Call storage.saveIdentity() which compares with stored key
4. If key changed → session is cleared atomically
5. Decryption proceeds with re-established session

This matches WhatsApp Web's behavior where extractIdentityKey is called
before handleNewSession (GysEGRAXCvh.js:40917, 48815).

Ref: WhatsApp Web's extractIdentityKey (GysEGRAXCvh.js:48976-48998)

src/Types/Auth.ts

@@ -81,6 +81,7 @@ export type SignalDataTypeMap = {
 	'lid-mapping': string
 	'device-list': string[]
 	tctoken: { token: Buffer; timestamp?: string }
+	'identity-key': Uint8Array
 }
 
 export type SignalDataSet = { [T in keyof SignalDataTypeMap]?: { [id: string]: SignalDataTypeMap[T] | null } }