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/read-file.ts

@@ -10,6 +10,11 @@ import { makeRelative, shortenPath } from '../utils/paths.js';
 import { BaseTool, ToolResult } from './tools.js';
 import { isWithinRoot, processSingleFileContent } from '../utils/fileUtils.js';
 import { Config } from '../config/config.js';
+import { getSpecificMimeType } from '../utils/fileUtils.js';
+import {
+  recordFileOperationMetric,
+  FileOperation,
+} from '../telemetry/metrics.js';
 
 /**
  * Parameters for the ReadFile tool
@@ -145,6 +150,19 @@ export class ReadFileTool extends BaseTool<ReadFileToolParams, ToolResult> {
       };
     }
 
+    const lines =
+      typeof result.llmContent === 'string'
+        ? result.llmContent.split('\n').length
+        : undefined;
+    const mimetype = getSpecificMimeType(params.absolute_path);
+    recordFileOperationMetric(
+      this.config,
+      FileOperation.READ,
+      lines,
+      mimetype,
+      path.extname(params.absolute_path),
+    );
+
     return {
       llmContent: result.llmContent,
       returnDisplay: result.returnDisplay,