Add CI testing using Github Actions

[Julow]

The OCaml community has the awesome ocaml-ci but for some reason we cannot enable it on this project until next week.

In the meantime, it would be useful to have a CI that does the following:

• Setup an OCaml environment with setup-ocaml
• Checkout the project source code.
• Install the project dependencies with opam install --deps-only -t -y .
• Run the tests with dune runtest.
• Check formatting with dune build @fmt.

This is a medium issue.

[maha-sachin]

@Julow Can you help to assign this issue?

[Julow]

@maha-sachin This issue is for you!

[maha-sachin]

@Julow, Thank you for assigning me this issue Add CI testing using GitHub Actions #37, I'll start working on it right away and keep you updated on my progress

[maha-sachin]

@Julow, When attempting to configure our CI workflow to run on the Windows environment (os: windows-latest) with the OCaml compiler version 4.14.0 (ocaml-compiler: "4.14.0"), I encountered an error during the setup process. Specifically, the error occurred while attempting to install dependencies, indicating a problem with resolving system dependencies for the diffcessible package.

Install system packages required by opam packages
  C:\Windows\system32\cmd.exe /D /S /C "D:\cygwin\wrapperbin\opam.cmd depext diffcessible"
  # Detecting depexts using vars: arch=x86_64, os=win32, os-distribution=cygwinports, os-family=windows
  [ERROR] No solution for diffcessible: The following dependencies couldn't be met:
            - diffcessible -> dune >= 3.11
                no matching version

  Command failed: opam list --readonly --external  "--resolve=diffcessible" returned 20
Error: The process 'D:\cygwin\wrapperbin\opam.cmd' failed with exit code 20

[Julow]

It seems that setup-ocaml on Windows uses an opam-repository (containing the definition of all the packages) that is too old and do not contain the version of Dune that we need. This is to be fixed later, for now, let's continue without Windows in the CI.

[Julow]

Done!