fix: use ring crypto backend for rustls cross-compilation

[justrach]

Summary

Switch from aws-lc-rs to ring as the crypto backend for rustls.

Problem

The aws-lc-rs crate fails to build when cross-compiling for aarch64-unknown-linux-gnu on GitHub Actions:

fatal error: stdatomic.h: No such file or directory
error: #error "ARM assembler must define __ARM_ARCH"

This happens because aws-lc-rs requires specific cross-compilation tools that aren't available in the CI environment.

Solution

Use ring instead of aws-lc-rs by setting:

rustls = { version = "0.23", default-features = false, features = ["ring", "std", "tls12"] }
tokio-rustls = { version = "0.26", default-features = false, features = ["ring"] }

ring is more portable and works out of the box for cross-compilation.

Test Plan

• CI builds pass for all targets including aarch64-linux