codebase_rag.utils.source_extraction:extract_source_lines not counting lines in file correctly

Seems to be ignoring a blank line, not counting it as a line of code when reading it in.

example of error message:
```codebase_rag.utils.source_extraction:extract_source_lines:28 - Line range 137-254 exceeds file length 102 in ...```

This would also mean that it's not properly generating proper semantic embeddings, since it would be grabbing the wrong code chunks when the error does not happen.
