Replace unmaintained paste crate with pastey

The paste crate is unmaintained (RUSTSEC-2024-0436). The author archived the repository.

Current usage: parser-core uses paste for macro token pasting.

Suggested fix: Replace with pastey, a maintained fork that's a drop-in replacement.

- paste = { workspace = true }
+ pastey = { workspace = true }

Then update macro invocations if needed (should be compatible).