Allow file scheme in RemoteArchive to simplify testing

[pstreef]

While it might look a bit controversial, the file scheme can also point to a remote (for instance a mounted network share) file. By allowing the file:// scheme we can use RemoteArchive for those files.

As a useful side effect, this makes testing RemoteArchive handling a lot easier.

What's changed?

RemoteArchive supports file:// protocol

What's your motivation?

Make it easier to test without having to manipulate the context and mocking

Anything in particular you'd like reviewers to focus on?

Do we want to allow file protocol for RemoteArchive

Anyone you would like to review specifically?

@sambsnyd

Have you considered any alternatives or workarounds?

Manipulate the context and mock the webserver

Any additional context

less mocking, more better!

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files