Add `NetBSD`, `OpenBSD` and `FreeBSD` CI testing using cross-platform action

[arthurbdiniz]

Description

It would be beneficial to include FreeBSD in our CI testing matrix to enhance platform compatibility. One potential approach is to use the Cross-Platform Action, which is also utilized by curl for their FreeBSD CI workflows.

For reference, curl's BSD CI configuration can be found here: Curl's CI Workflow.

Tasks

1. Investigate the feasibility of integrating NetBSD, OpenBSD and FreeBSD tests using Cross-Platform Action.
2. Draft a CI workflow configuration for NetBSD, OpenBSD and FreeBSD.
3. Test the workflow and refine as needed.
4. Create a pull request for review.

Outcome

This enhancement will improve our project's robustness across platforms.