fix(realtime): terminate web worker on disconnect

[tanmaysharma2001]

🔍 Description

Fixes a critical memory leak in RealtimeClient where Web Workers created with the worker: true option were never terminated on disconnect, causing workers to accumulate indefinitely in long-running applications.

What changed?

• Added a new private method _terminateWorker() in RealtimeClient.ts that properly terminates the Web Worker with error handling
• Updated _teardownConnection() to call _terminateWorker() during connection cleanup
• Worker termination now happens alongside other resource cleanup (timers, channels)

Why was this change needed?

Web Workers were being created in _startWorkerHeartbeat() (line 691) but never terminated in _teardownConnection() (line 628-649). Each disconnect/reconnect cycle would leak one worker, causing memory accumulation over time.

Impact:

• Affects anyone using RealtimeClient with worker: true option
• Critical for long-running applications (SPAs, Electron apps) with multiple connection cycles
• Memory leak: ~10-50KB per orphaned worker (browser-dependent)

Reproduction:

const client = new RealtimeClient(url, { params: { apikey }, worker: true })

for (let i = 0; i < 10; i++) {
  client.connect()
  await new Promise(resolve => setTimeout(resolve, 1000))
  client.disconnect() // Worker leaked here ❌
}
// 10 workers still running after this loop

Closes #1902

📸 Screenshots/Examples

Before this fix:

// Worker created but never terminated
private _teardownConnection(): void {
  // ... connection cleanup ...
  this._clearAllTimers()
  // ❌ Missing: worker termination
  this.channels.forEach((channel) => channel.teardown())
}

After this fix:

// Worker properly terminated with error handling
private _terminateWorker(): void {
  if (this.workerRef) {
    try {
      this.workerRef.terminate()
      this.log('worker', 'worker terminated')
    } catch (e) {
      this.log('error', 'Error terminating worker', e)
    } finally {
      this.workerRef = undefined
    }
  }
}

private _teardownConnection(): void {
  // ... connection cleanup ...
  this._clearAllTimers()
  this._terminateWorker()  // ✅ Worker properly cleaned up
  this.channels.forEach((channel) => channel.teardown())
}

🔄 Breaking changes

• [☑️] This PR contains no breaking changes

📋 Checklist

• [☑️ ] I have read the Contributing Guidelines
• [☑️] My PR title follows the conventional commit format: <type>(<scope>): <description>
• [☑️] I have run npx nx format to ensure consistent code formatting
• [☑️] I have added tests for new functionality (if applicable)
• [☑️] I have updated documentation (if applicable)

📝 Additional notes