Is it possible to find the date of a change?

Unless you go to poke the `crates.io` HTTP API, the only way to find the publication date of a particular version of a crate is to grovel through the index git repository. I'm going to need to do this eventually, but since this project already does a bit of groveling through the index git repository, would you be interested if I just contributed a PR to add this functionality?

Start by reading the existing code that traverses the crates.io index git repository and compare it with the crates.io HTTP API's publication-date data. Define how the project should expose the date for a particular crate version, then verify that the result matches the registry data; the issue names no files or tests to run.

Written by the indexing model from the issue text.