fix: filter out test diffs with None test_src_code

[misrasaurabh1]

Summary

• Filter out test diffs where test_src_code is None before calling the code_repair API endpoint
• Return early with a warning log if no valid test diffs remain after filtering

Problem

When running codeflash on JavaScript/TypeScript files, the code_repair API call fails with:

ERROR    Error generating optimized candidates: 422 - {"detail": [{"type":      
         "string_type", "loc": ["body", "data", "test_diffs", 0,                
         "test_src_code"], "msg": "Input should be a valid string"}]}

This happens because:

1. The CLI's TestDiff.test_src_code is Optional[str] = None
2. The get_src_code() method returns None when it can't find/parse the test source
3. The aiservice expects test_src_code: str (non-nullable)

Test plan

• Manual testing with codeflash on appsmith TypeScript codebase
• Unit test to verify filtering logic works correctly

🤖 Generated with Claude Code

[misrasaurabh1]

@aseembits93 can you review this? why would this be None? is there a root cause fix for this?

[aseembits93]

@misrasaurabh1 this is the expected schema on the backend

class TestDiff(Schema):
    test_src_code: str

this is the schema on cli

@dataclass
class TestDiff:
    test_src_code: Optional[str] = None

i'll fix it on the backend, we can close this one