package: add x64 macOS codex-zsh artifact

[bolinfest]

Why

The package builder has an Intel macOS release target (x86_64-apple-darwin) whose DotSlash platform is macos-x86_64, but scripts/codex_package/codex-zsh only listed Apple Silicon macOS plus Linux platforms. Because zsh is fetched with missing_ok=True, Intel macOS packages could miss the patched zsh resource instead of resolving a prebuilt artifact.

The rust-v0.134.0-alpha.3 release now publishes codex-zsh-x86_64-apple-darwin.tar.gz, so the manifest can cover that platform. See the release assets in https://github.com/openai/codex/releases/tag/rust-v0.134.0-alpha.3 and the completed release job at https://github.com/openai/codex/actions/runs/26319528477/job/77485808896.

Relevant existing mappings:

• x86_64-apple-darwin maps to macos-x86_64: https://github.com/openai/codex/blob/main/scripts/codex_package/targets.py#L88-L93
• zsh resources are resolved from scripts/codex_package/codex-zsh: https://github.com/openai/codex/blob/main/scripts/codex_package/zsh.py#L14-L22

What Changed

• Updated existing codex-zsh DotSlash entries to rust-v0.134.0-alpha.3 release URLs and refreshed their size and SHA-256 metadata.
• Added a macos-x86_64 entry for codex-zsh-x86_64-apple-darwin.tar.gz.

Verification

• Downloaded the four codex-zsh-*.tar.gz release assets from rust-v0.134.0-alpha.3, computed their wc -c sizes and shasum -a 256 digests, and verified each archive contains codex-zsh/bin/zsh.
• python3 -m unittest discover -s scripts/codex_package -p 'test_*.py'