refactor: use native DepotDownloader, removing dotnet as a requirement

[timkurvers]

This PR downloads a native DepotDownloader build from GitHub (arm64 or x64), effectively removing the requirement for dotnet.

Should hopefully solve both #74 and #75. Will wait a bit before merging this in, just to make sure this variation works for others.

---

To try this variant of the build script:

git pull # or `git fetch` may suffice
git checkout refactor/remove-dotnet-requirement
./build.sh

If you'd like to swap back to the stable variant, git checkout main again.

[ProfAronnax]

Hi @timkurvers , thanks! That worked fine for me now thanks for the quick help and you work to make Valheim playable direct with Mac.

[timkurvers]

Thanks for testing! 👍 Have merged this in (make sure to swap back to main).