[hpke-rs-rust-crypto] macOS builds don't use AES HW-accelerated instructions #1583

The current version of the HPKE rust crypto provider relies on the version 0.10 of the aes-gcm crates, which itself relies on the version 0.8 of the aes crate. As a result, when building hpke-rs with Rust crypto and relying on AES-GCM, by default, the fixed-slice software-only implementation of AES is used, with suboptimal performances.

A possibility consists in bumping the aes-gcm dependency to 0.11, which itself depends on aes v0.9 that implements underlying HW capabilities auto-detection on macOS.

In the meanwhile, a workaround consists in explicitly setting a configuration flag at the compiler level, possibly with side effects wrt to other crates:

[target.aarch64-apple-darwin]
rustflags = ["-C", "target-cpu=native", "--cfg", "aes_armv8"]