Handle telemetry in non-interactive mode (#1002)

Changes:
- Ensure proper shutdown in non-interactive mode
- Ensures the initial user prompt is logged in non-interactive mode
- Improve telemetry for streaming - handle chunks and input token count is now alongside other token counts in response

To test:
- Follow instructions in https://github.com/google-gemini/gemini-cli/blob/main/docs/core/telemetry.md#google-cloud
- Run CLI in non-interactive mode and observe logs/metrics in GCP Logs Explorer and Metrics Explorer

#750

packages/core/src/utils/requestUtils.ts

@@ -1,15 +0,0 @@
-/**
- * @license
- * Copyright 2025 Google LLC
- * SPDX-License-Identifier: Apache-2.0
- */
-
-import { Content } from '@google/genai';
-
-export function getRequestTextFromContents(contents: Content[]): string {
-  return contents
-    .flatMap((content) => content.parts ?? [])
-    .map((part) => part.text)
-    .filter(Boolean)
-    .join('');
-}