Support lockfile version 4

[ericcornelissen]

I just tried cargo-goggles@v0.0.2 on one of my project and found it did not work because the lockfile version was 4 (just like this project, actually). This version has become the default since Cargo 1.83.

The exact error I get from cargo-goggles is:

$ cargo goggles
Error: decode Cargo.lock

Caused by:
    parse error: parse error: invalid Cargo.lock format version: `4`

I'm just opening this issue for visibility and as a reminder to add support for the newer lockfile format.