fix: strip file extensions from JS/TS import paths in generated tests

[misrasaurabh1]

Summary

Fixes the root cause of "Cannot find module" errors when running JS/TS tests.

The add_js_extension() function in module_system.py was adding .js extensions when converting CommonJS require() to ESM import statements. TypeScript and Jest don't require explicit extensions and adding them causes module resolution failures.

Problem

When the CLI converted CommonJS to ESM:

// Before (CommonJS from aiservice)
const { func } = require('../utils/helper');

// After conversion (ESM with added .js - WRONG!)
import { func } from '../utils/helper.js';

This caused:

Cannot find module '../utils/helper.js' from 'test/test.ts'

Solution

Modified add_js_extension() to NOT add extensions. TypeScript and modern bundlers handle extension resolution automatically.

Note: Extension stripping for LLM-generated tests is now handled by the aiservice (see codeflash-internal PR #2341).

Test plan

• All existing tests pass
• Manual testing confirms no more "Cannot find module" errors

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