feat: CLI interface and unit tests

[Rakshitha-Ireddi]

Summary

• CLI interface (cli.py + pyproject.toml entry point): Users can now run the tool directly from the terminal
  without editing Python source files.
• Unit tests (tests/): 30 tests across test_utilities.py and test_main.py covering all core logic with zero
  heavy model dependencies.

CLI usage

Gemini (default):

llm-wer \
  --dataset predictions.csv \                                                                                         
  --ref-col transcription \                               
  --pred-col prediction \                                                                                             
  --audio-col audio_filepath \
  --creds-path service_account.json                                                                                   

Any OpenAI-compatible API:

  llm-wer \
    --dataset predictions.csv \
    --ref-col transcription \                                                                                           
    --pred-col prediction \  
    --audio-col audio_filepath \                                                                                        
    --no-gemini \                                           
    --model gpt-4o \
    --api-key sk-... \
    --base-url https://api.openai.com/v1                                                                                

With Google Sheets output:
llm-wer ... --sheet-name "LLM WER Analysis" --worksheet-name "run-1"

Install with: pip install -e ".[dev]" then run llm-wer --help.

Tests

tests/
├── test_utilities.py # wer(), cer() — edge cases, custom weights, clamping
└── test_main.py # get_segments(), build_prompt(), process_llm_responses(),
# reconstruct_and_score(), load_and_validate_dataset()

Run with: pytest (no heavy model downloads required — normalizer/LLM calls are not exercised).

Test plan

• pip install -e ".[dev]" && pytest — all 30 tests pass
• llm-wer --help — shows full usage
• llm-wer --no-gemini --model gpt-4o --api-key ... --base-url ... — routes to OpenAI
• Omitting --sheet-name — no Sheets upload attempted