Fetch pre-compiled rebar3 instead of building it locally

[kivra-pauoli]

This is a partial fix for #15, as well as (hopefully) issues with e.g. escript not being available at compile-time, as described in asdf-vm/actions#585.

Advantages

• faster build time (no build, actually 😄)
• wider Erlang version range - compatibility (since it's build for Erlang by erlang/rebar3): "The 3 newest major Erlang releases are supported at any given time: if the newest version is OTP-27, building with versions as old as OTP-25 will be supported, and produce an executable that will work with those that follow."

[kivra-pauoli]

Probably best seen with Hide whitespace enabled as part of this included changes in formatting.

[kivra-pauoli]

I'll also update CI to use asdf-vm/actions and thus replicate a real user situation (erlang installed via asdf plugin)...

Edit: was trying to update the tests to work around the scenario described over at asdf-vm/actions#585, but ran into a similar issue: https://github.com/kivra-pauoli/asdf-rebar/actions/runs/10819613897/job/30017898426#step:5:46; the escript shim is available (https://github.com/kivra-pauoli/asdf-rebar/actions/runs/10819613897/job/30017898426#step:4:7152) but not even a reshim before rebar3 --version helps the test.

Edit: the workflow file for that run can be seen here.

[Stratus3D]

Thanks for the PR @kivra-pauoli ! Looks good to me. I'm going to do some testing and then merge later.

[Stratus3D]

Tested locally and seems good to me. And much faster!