Feature: Add Vitest unit test framework

[brunomenezes]

Summary

Add Vitest as our unit test framework. Also, include the first test cases and update the GitHub actions to run the tests.

Changes:

• Added Vitest as unit test framework
• Added coverage-v8 module for coverage generation (when passing the --coverage Vitest suggested to install that, so no brainer)
• Added test cases for the processor focused on createProcessor factory function.

PS: I will create issues for adding tests for the handlers and also one to publish the coverage report with coveralls.