Only call 3dslink if a runner is not configured

[ian-h-chamberlain]

Follow-up to #60 which I believe broke cargo test and cargo run when a custom runner is configured...

#49 would probably have caught this if we ran some tests in CI — I will see if it's not too hard to add some kind of dummy crate to test against for those cases (integration tests, examples etc.)

[Meziu]

LGTM, though I find all of the pub(crate) diffs a bit funny 😆.

[ian-h-chamberlain]

LGTM, though I find all of the pub(crate) diffs a bit funny 😆.

Yeah, I couldn't think of a better way to try and catch more dead code (like the fn I deleted). See https://stackoverflow.com/a/51636336/14436105 and rust-lang/rust#74970, rust-lang/rust#120079

pub(crate) seemed easiest to make sure everything still compiled, but some of those could also be probably be made private. An alternative as mentioned in some of those issues would be to move lib.rs to a submodule of main instead, which but that feels a bit awkward and I'm not sure if it would really help that much anyway.