Builder constructor should take arguments

[yoshuawuyts]

I was looking at #1746, and I realized that we've made it so the builder takes its arguments as part of the .build method rather than as part of the constructor. This means we have an API like this:

SandboxBuilder::new().build_from_file(hyperlight_guest_path.clone())?;

Instead in Rust it's more common to have the builder constructor take the arguments, for example like with ContextBuilder::from_waker. Adapted to our builder that would change the API to:

SandboxBuilder::from_file(hyperlight_guest_path.clone()).build()?;

It's not a huge difference, but it is just a little shorter, and at least matches my expectations a bit better. @jprendes what do you think?

[jprendes]

That sounds good.

The only caveat is that build_from_bytes takes a &[u8]. With the current approach we don't have to handle ref's lfetimes explicitly. If we have it as an argument we would need to add a lifetime generic to the builder.

[jprendes]

Ok, I can change the internal API to take a Vec<u8> instead of a &[u8] without any penalty (we were converting the &[u8] to a Vec<u8> later on anyway)