STT Evaluation: UX Enhancements

[AkhileshNegi]

Is your feature request related to a problem?
The current STT Evaluation has few areas for improvement that enhance user experience

Describe the solution you'd like

• Implement per sample language selection that falls back to the dataset language
• Allow users to choose null in STT eval result annotation if 'yes' or 'no' is selected by mistake
• Ensure consistency in displaying UI STT results even when ground truth is missing