fix: patch Darwin liblzma linkage

[houseme]

Summary

Fix the aarch64-darwin package so the prebuilt RustFS binary no longer depends on Homebrew's absolute liblzma path at runtime.

Root Cause

The upstream macOS aarch64 release binary currently contains this Mach-O load command:

/opt/homebrew/opt/xz/lib/liblzma.5.dylib

The flake installs the downloaded binary unchanged, so packages.aarch64-darwin.default can fail in a clean Nix environment where Homebrew's xz is not installed at that exact path.

Changes

• Add Darwin-only install_name_tool support during the package install phase.
• Copy Nixpkgs' xz liblzma.5.dylib into $out/lib.
• Rewrite the RustFS binary to load @executable_path/../lib/liblzma.5.dylib.
• Leave Linux package behavior unchanged.

Validation

• git diff --check
• jq empty sources.json
• actionlint
• Ruby YAML parse for .github/workflows/*.yml
• PR CI passed:
  • Lint and Evaluate
  • Build Linux package
• Local Mach-O patch simulation against the current 1.0.0-beta.12 macOS aarch64 asset:
  • source zip SHA256 matched sources.json
  • otool -L changed from /opt/homebrew/opt/xz/lib/liblzma.5.dylib to @executable_path/../lib/liblzma.5.dylib
  • codesign --verify --verbose remained valid
  • patched $out/bin/rustfs --help ran successfully

Local nix is not installed in this checkout environment, and the existing repository CI does not include a macOS package build job. A full nix build .#packages.aarch64-darwin.default still needs to be run in a Nix-enabled macOS environment.

Fixes #51.