chore: CI - build - reusable workflow artifacts

[dulmandakh]

This PR introduces build workflow that other workflows should depend to re-use build artifacts as cache to save time. Once this PR lands confirming that we can save time using build artifacts, I'll work on CI optimization utilizing turbo caching.

[dulmandakh]

@aqrln please approve workflows

[Copilot]

Pull Request Overview

This PR introduces a dedicated build workflow that other CI workflows will depend on to reuse build artifacts as cache, aiming to optimize CI performance by avoiding redundant builds.

Key changes:

• Creates a new Build workflow that runs on pull requests and builds across multiple Node.js versions
• Updates bundle-size workflow to depend on the Build workflow completion via workflow_run trigger
• Adds turbo caching setup in the shared setup action to enable build artifact reuse

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/build.yml	New workflow that builds the project across Node.js versions 18, 20, 22, and 24
.github/workflows/bundle-size.yml	Updated to trigger after Build workflow completion and re-enabled TSC and build steps
.github/actions/setup/action.yml	Added turbo cache configuration and offline-preferred pnpm install

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[Copilot]

The paths-ignore configuration at line 8 will not work with workflow_run triggers. The paths-ignore filter only applies to direct event triggers like pull_request or push, not to workflow_run events. Consider moving the path filtering logic to the Build workflow or using conditional job execution based on changed files.

[Copilot]

Using github.sha in the cache key means each commit will create a new cache entry, preventing cache reuse across commits. Consider using a more stable key like ${{ hashFiles('**/pnpm-lock.yaml', 'turbo.json') }} to enable cache sharing between commits with the same dependencies and turbo configuration.

Suggested change

	key: ${{ runner.os }}-node-${{ inputs.node-version }}-turbo-${{ github.sha }}
	key: ${{ runner.os }}-node-${{ inputs.node-version }}-turbo-${{ hashFiles('**/pnpm-lock.yaml', 'turbo.json') }}