Add file operation telemetry (#1068)

Introduces telemetry for file create, read, and update operations.

This change adds the `gemini_cli.file.operation.count` metric, recorded by the `read-file`, `read-many-files`, and `write-file` tools.

The metric includes the following attributes:
    - `operation` (string: `create`, `read`, `update`): The type of file operation.
    - `lines` (optional, Int): Number of lines in the file.
    - `mimetype` (optional, string): Mimetype of the file.
    - `extension` (optional, string): File extension of the file.

Here is a stacked bar chart of file operations by extension (`js`, `ts`, `md`):
![image](https://github.com/user-attachments/assets/3e8f8ea9-6155-4186-863c-075cc47647c5)

Here is a stacked bar chart of file operations by type (`create`, `read`, `update`):
![image](https://github.com/user-attachments/assets/3fcf491d-31d0-4ba8-80e6-7fd2bd9c7c27)

#750 

cc @allenhutchison as discussed

packages/core/src/tools/write-file.ts

@@ -26,6 +26,11 @@ import {
 import { GeminiClient } from '../core/client.js';
 import { DEFAULT_DIFF_OPTIONS } from './diffOptions.js';
 import { ModifiableTool, ModifyContext } from './modifiable-tool.js';
+import { getSpecificMimeType } from '../utils/fileUtils.js';
+import {
+  recordFileOperationMetric,
+  FileOperation,
+} from '../telemetry/metrics.js';
 
 /**
  * Parameters for the WriteFile tool
@@ -271,6 +276,27 @@ export class WriteFileTool
 
       const displayResult: FileDiff = { fileDiff, fileName };
 
+      const lines = fileContent.split('\n').length;
+      const mimetype = getSpecificMimeType(params.file_path);
+      const extension = path.extname(params.file_path); // Get extension
+      if (isNewFile) {
+        recordFileOperationMetric(
+          this.config,
+          FileOperation.CREATE,
+          lines,
+          mimetype,
+          extension,
+        );
+      } else {
+        recordFileOperationMetric(
+          this.config,
+          FileOperation.UPDATE,
+          lines,
+          mimetype,
+          extension,
+        );
+      }
+
       return {
         llmContent: llmSuccessMessage,
         returnDisplay: displayResult,