Dashu depends on crate `paste` flagged by RustSec as no longer maintained

[remi-delmas-3000]

Hello, while auditing code that uses dashu I realized dashu depends on paste that is no longer maintained

Crate:     paste
Version:   1.0.15
Warning:   unmaintained
Title:     paste - no longer maintained
Date:      2024-10-07
ID:        RUSTSEC-2024-0436
URL:       https://rustsec.org/advisories/RUSTSEC-2024-0436
Dependency tree:
paste 1.0.15
└── dashu-macros 0.4.1
    └── dashu 0.4.2

it seems like pastey could be a drop in replacement for paste. I created a PR for the modification #58