@spec get_metrics(binary()) :: [map()]

Returns aggregated metrics for all versions of a prompt.

Returns list of maps with structure:

• version_id: binary_id
• version_number: integer
• created_at: datetime
• total_runs: integer (suite runs only)

• avg_pass_rate: float | nil

• avg_cost_usd: Decimal.t() | nil

• avg_latency_ms: integer | nil

• provider_breakdown: list of provider-specific metrics

@spec prepare_chart_data([map()]) :: map()

Prepares metrics data for Chart.js visualization.

Returns map with structure:

• versions: list of version numbers
• overall: aggregated metrics across all providers
• by_provider: metrics grouped by provider name