Add reusable test & coverage CI workflow

[wonderwomancode]

Summary

Add a reusable GitHub Actions workflow (.github/workflows/test.yml) that standardizes test + coverage runs across all AF repos.

Inputs

• node-version (default: 20)
• pnpm-version (default: 9)
• build-before-test (default: false)
• test-command (default: pnpm test:coverage)

Steps

• Checkout, setup Node + pnpm with caching, install, optionally build, run tests, upload coverage artifact

Used by: service-cloud-api, service-auth, package-cloud-sdk, package-cloud-cli

[wonderwomancode]

@mavisakalyan — PR ready for review: #17

Merge order: This PR must merge first before the dependent PRs in other repos:

• feat: add test coverage thresholds and CI workflow alternate-clouds-api#134
• feat: add test coverage thresholds and CI workflow alternate-clouds-auth#73
• feat: add test coverage thresholds and update CI workflow alternate-clouds-sdk#18
• alternatefutures/package-cloud-cli#63