Add vitest config

[Amorim33]

Description

We need automated tests as soon as possible in the core. Tests ensure not only quality but also accelerate development, a strong culture of automated testing makes the team more agile and with more bug-free deliveries.

We already have some tests ( e.g. https://github.com/expressots/expressots/blob/main/packages/core/test/application.spec.ts), but they are not running correctly.

The goal of this issue is to fix the config and enable tests to run, it also should use Vitest instead of Jest, they are almost the same in terms of syntax. However, Vitest is much faster.

Ref.
https://vitest.dev/
https://vitest.dev/config/
https://dev.to/mbarzeev/from-jest-to-vitest-migration-and-benchmark-23pl

Requirements

• vite and vitest must be listed in the project references;
• all tests must run;
• tests must run in the CI.

Definition of Done

• assert that tests are running correctly using vitest;
• assert that the action is correctly running in the PR.