feat(utils): centralize CPC and metrics calculation with computeCPCMetrics

[byteakp]

✨ Centralize CPC and Metrics Calculation Logic

This PR introduces a new utility function, computeCPCMetrics, in @adobe/spacecat-shared-utils to centralize the logic for calculating CPC (Cost Per Click) and related metrics using organic traffic and RUM data. This logic was previously duplicated across multiple services.

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🔧 Key Changes

• New Utility Function

  • computeCPCMetrics is now available in @adobe/spacecat-shared-utils.
  • Accepts current and total RUM metrics and an array of organicTraffic metrics.
  • Returns:
    • cpc
    • pageViewsChange
    • ctrChange
    • projectedTrafficValue

• Documentation

  • Updated API.md and README.md to include usage examples.
  • Updated index.d.ts with full type annotations for clarity.

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💡 Motivation

• 🚫 Removes duplicated CPC computation logic from:
  • spacecat-api-service
  • spacecat-import-worker
• ✅ Provides a single, reusable, and testable utility for computing CPC-related metrics.

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🧩 Usage

import { computeCPCMetrics } from '@adobe/spacecat-shared-utils';

const { cpc, pageViewsChange, ctrChange, projectedTrafficValue } = computeCPCMetrics({
  current: { totalPageViews, totalClicks, totalCTR },
  total: { totalPageViews, totalClicks, totalCTR },
  organicTraffic: [{ cost, value }],
});