fix: validate JS/TS functions are exported before optimization

[misrasaurabh1]

Summary

• Adds validation to check if JavaScript/TypeScript functions are exported before attempting optimization
• Non-exported functions cannot be imported by tests, making optimization impossible
• Shows a clear error message explaining the issue and how to fix it

Problem

Previously, codeflash would generate tests that try to import non-exported functions, leading to confusing runtime errors like:

TypeError: codeflash.capture: Expected function 'foo' but got undefined.
This usually means the function was not imported correctly.

Solution

Now codeflash validates export status early and shows a helpful error message:

Function 'getEnvLogLevel' is not exported from src/utils/AppUtils.ts.
In JavaScript/TypeScript, only exported functions can be optimized
because tests need to import them.
To fix: Add 'export' keyword to the function declaration, e.g.:
  export const getEnvLogLevel = ...

Test plan

• Existing tests pass (pytest tests/test_languages/test_import_resolver.py -v)
• Manual testing with non-exported function shows correct error message
• Manual testing with exported function proceeds to optimization normally

🤖 Generated with Claude Code