ci: add aarch64-unknown-linux-gnu target to release builds

[Cyrah2R]

This PR adds support for automatically building and releasing aarch64-unknown-linux-gnu binaries for Linux.

With the growing adoption of ARM-based cloud instances (AWS Graviton, Oracle Cloud, etc.), having pre-compiled aarch64 releases will save users from having to install the Rust toolchain on their production servers just to compile c2patool.

Changes made

1. .github/workflows/release.yml: Added the aarch64 target to the release matrix and included a step to install gcc-aarch64-linux-gnu for cross-compilation on the Ubuntu runner. Passed the ARCH=aarch64 flag to the make release command when needed.
2. cli/Makefile: Updated the Linux release targets to check for the ARCH=aarch64 flag. If present, it adds the appropriate rustup target, uses the aarch64 linker, and packages the tarball with the correct _linux_aarch64 naming convention so it doesn't conflict with the Intel build.

Closes #1997

[Cyrah2R]

Hi Eric,

Thank you! I just pushed a new commit updating docs/support-tiers.md. I noticed there was a small typo (aarch- instead of aarch64-) for the Ubuntu (ARM) targets in the Tier 1B sections, so I went ahead and corrected it across all three components to match the official aarch64-unknown-linux-gnu target we are using for the release.

Let me know if everything looks good!