feat: add identity change handler for improved connection stability

Cherry-pick from upstream PR #2264 (commit 5cbad317) with enhancements:

## Changes

### New Files
- `src/Utils/identity-change-handler.ts`: Centralized identity change handling
  - Enterprise-grade JSDoc documentation
  - Clear result types for all 9 possible outcomes
  - Debouncing to prevent duplicate session refreshes
  - Companion device filtering
  - Offline notification handling

- `src/__tests__/Socket/identity-change-handling.test.ts`: Comprehensive tests
  - Core functionality tests
  - Debounce behavior tests
  - Error handling tests
  - Edge case coverage

### Modified Files
- `src/Socket/messages-recv.ts`: Updated error handling
  - MISSING_KEYS_ERROR now returns NACK with ParsingError
  - Maintains CTWA recovery logic intact
  - Preserves all Prometheus metrics integration

- `src/Utils/generics.ts`: Added `isStringNullOrEmpty()` helper
- `src/Utils/index.ts`: Added identity-change-handler export

## Benefits
- Fixes "Online" status shown when actually disconnected (#2132)
- Better session management after contact identity changes
- Clear separation of concerns with dedicated handler module

Co-authored-by: João Lucas de Oliveira Lopes <55464917+jlucaso1@users.noreply.github.com>

src/Utils/generics.ts

@@ -50,6 +50,10 @@ export const BufferJSON = {
 export const getKeyAuthor = (key: WAMessageKey | undefined | null, meId = 'me') =>
 	(key?.fromMe ? meId : key?.participantAlt || key?.remoteJidAlt || key?.participant || key?.remoteJid) || ''
 
+export const isStringNullOrEmpty = (value: string | null | undefined): value is null | undefined | '' =>
+	// eslint-disable-next-line eqeqeq
+	value == null || value === ''
+
 export const writeRandomPadMax16 = (msg: Uint8Array) => {
 	const pad = randomBytes(1)
 	const padLength = (pad[0]! & 0x0f) + 1