coverage: define test suite with unit tests

[danctorres]

Description

• Added a test suite to support coverage reporting.
• Updated the documentation to include detailed instructions on how to add tests for coverage, including best practices for organizing tests and integrating them into the unit_tests suite.

Checklist

• Code follows project style guidelines.
• Documentation updated (if applicable).
• Tested in simulation/real-world environment (if applicable).

Testing

Tested locally, by generating a coverage report with:

bazel run //tools/coverage:lcov -- -t :unit_tests

and CI github action.

Related Issue

Issue: #106

Notes

To do on a follow-up task:

• Generate coverage report with baseline.
• Gating mechanism for coverage.