Log Message:
lang/rust: Allow arbitrary + sub-versions in rust crates

From: Taylor R Campbell <riastradh@NetBSD.org>

Before, a crate name like wasi-0.11.0+wasi-snapshop-preview1.crate
(which has non-numeric/dot characters after the + delimiter) would be
mapped to the URL:

https://crates.io/api/v1/crates/wasi/wasi-0.11.0+wasi-snapshot-preview1/download

when the correct URL is:

https://crates.io/api/v1/crates/wasi/0.11.0+wasi-snapshot-preview1/download

Extension of the fix discussed on tech-pkg@ at:
https://mail-index.NetBSD.org/tech-pkg/2025/03/16/msg030612.html