fix(deps): migrate from proc-macro-error to proc-macro-error2

[welpo]

Migrate from proc-macro-error to proc-macro-error2

Overview

Replaces the proc-macro-error crate with proc-macro-error2, an actively maintained fork.

Resolves #425.

Changes

• Replace proc-macro-error with the latest version of proc-macro-error2 in Cargo.toml
• Replace proc-macro-error references with proc-macro-error2

Motivation

The proc-macro-error crate has been flagged as unmaintained (RUSTSEC-2024-0370). Migrating to proc-macro-error2 addresses this security advisory and ensures our project uses an actively maintained dependency.

Testing

• All existing tests have been updated and pass