io: Implement skip_until

[WilliamVenner]

Motivation

std::io::BufRead::skip_until was stabilized in Rust 1.83.0. Let's implement it into Tokio, too.

Solution

I have simply adapted existing read_until code to discard the read bytes rather than writing them in to a buffer.

[ADD-SP]

This breaks the MSRV, current MSRV is Rust 1.70, this requires 1.83.