zig: backport to fix caching zip files

[cho-m]

Specifically to explore splitting out fetch phase

  deny_network_access!

  def fetch
    system "zig", "build", "--fetch=all"
  end

  def install
    system "zig", "build", "--system", "zig-pkg", *std_zig_args
  end

Gentoo as reference for separate phases: https://github.com/gentoo/gentoo/blob/master/eclass/zig.eclass

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• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>?
• Is your test running fine brew test <formula>?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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[github-actions]

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