Add Model harness with WER score and tests (STT)

[Blaizzy]

Description

We need to implement a model harness for evaluating Speech-to-Text (STT) models that calculates Word Error Rate (WER) as the primary performance metric, along with comprehensive tests.

Requirements

• Implement a model harness that can load and evaluate any STT model in our system
• Calculate WER (Word Error Rate) as the primary metric
• Support additional metrics where appropriate (CER, BLEU, etc.)
• Provide test utilities to generate synthetic audio for testing edge cases
• Create benchmark test suite with standard datasets (LibriSpeech, Common Voice, etc.)
• Support different audio formats and sampling rates
• Generate comprehensive reports with per-utterance and aggregate scores

Acceptance Criteria

• [x] Model harness successfully loads and evaluates STT models
• [x] WER calculation matches reference implementation (tested against known examples)
• [x] Test suite covers at least 3 standard STT datasets
• [x] Documentation includes examples and explanation of metrics
• [x] CI integration ensures WER doesn't regress on benchmark datasets