Remove proc-macro-error2 dependency?

[avandecreme]

That dependency has been marked as unmaintained, see https://rustsec.org/advisories/RUSTSEC-2026-0173

Instead of finding a replacement, I believe it would be better to just get rid of it.

I am willing to look into implementing that if you agree.

[divarvel]

The advisory also mentions two alternatives, but yeah maybe vendoring it could be ok.

No pressure on this, but if you're willing to look into it, that would be welcome (as long as there is no regression in DX)

[FBranca]

The linked pull request contains a remplacement with one of them (manyhow)