feat: Reusable workflow for monorepo with matrix of jobs

Description

Add a workflow that can be integrated into Dart/Flutter repositories. When triggered, it scans the repository and runs the same checks on every package it finds.

Steps:

• Scan the repository and list all packages.
• Identify which packages need to be tested and generate a job matrix.
• Run verifications (e.g., tests, analysis).

The workflow should also be customizable per package—for example, allowing different coverage thresholds.

Note:
This workflow should only run the core steps for each package. If a package has additional checks, those should be defined in a separate workflow.

Goals:

• Avoid creating a new workflow file for each package.
• Simplify maintenance of core checks.
• Ensure the same checks are enforced for newly added packages.

Requirements

• All CI/CD checks are passing.
• There is no drop in the test coverage percentage.

Additional Context

No response