server: Replace usage of once_cell with equivalent from std

[future-highway]

Drop the direct dependency on once_cell as equivalent functionality was released in std for Rust 1.80 (July 25, 2024).

Motivation

Eventually this will hopefully lead to 1 less dependency, however for now once_cell still remains as an indirect dependency since it is used widely in the ecosystem.

Solution

Replace usage of once_cell::sync::Lazy with std::sync::LazyLock.