[FEATURE] Add Stryker Mutation Testing to CI Pipeline

[AndrewBarber]

Is your feature request related to a problem? Please describe.
We currently lack comprehensive test coverage validation in our CI pipeline. While our unit tests verify basic functionality, we don't have a way to assess the quality and effectiveness of our test suite systematically.

Describe the solution you'd like
Integrate Stryker Mutation Testing into our CI pipeline to:

• Run mutation tests automatically on pull requests
• Set a minimum mutation score threshold (80%)
• Generate and store mutation test reports as artifacts
• Add mutation score badges to our README

Example Usage

jobs:
  mutation:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20.x'
      - run: npm ci
      - run: npx stryker run

Additional context
Current mutation score: 77.27%
Target mutation score: 80%+