Lower tok Rust MSRV to 1.77.2

[t-kalinowski]

Summary

This updates tok to build with Rust 1.77.2, matching CRAN's requirement that submitted packages support a Rust toolchain at least two years old.

Public-facing changes:

• Lowers the declared Rust requirement from rustc >= 1.91 to rustc >= 1.77.2.

Internal changes:

• Downgrades the Rust tokenizers dependency from 0.22.2 to 0.20.4, the newest version tested here that builds on Rust 1.77.2.
• Refreshes Cargo.lock and src/rust/vendor.tar.xz for the compatible dependency graph.
• Regenerates bundled Rust dependency author/license metadata.
• Skips the Hugging Face network test when huggingface.co is unreachable, so non-CRAN offline checks do not fail for unrelated DNS/network reasons.

[dfalbel]

thanks!