Track proc-macro-error2 unmaintained audit problems

[mulkieran]

At present our source has a lot of dependencies on this officially unmaintained crate: https://rustsec.org/advisories/RUSTSEC-2026-0173 .

Most of these dependencies are through the env_logger crate, which is a standby for plenty of crates.

We have no way to shed this dependency at this time, so we will have to just accept releases that are encumbered by this advisory. But we should shed it once we can.

[jbaublitz]

@mulkieran I maintain getset and this was the RUSTSEC alert that I referenced needing to work on. I guess it's more widespread in the community than I realized.