Prepare combined upgrade planning

[MikeMcQuaid]

• return successful formula and cask upgrades to callers
• retain prefetched installers and dependant download plans
• deduplicate package summaries before execution

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[Copilot]

Pull request overview

This pull request prepares brew upgrade for combined/batched upgrade planning by making upgrade routines return richer results and by enabling reuse of prefetched installers and download plans across steps.

Changes:

• Refactors formula installer selection for dependents and adds helper APIs to reuse prefetched FormulaInstaller instances.
• Extends formula upgrades with a cleanup: switch to allow deferring cleanup until after a batch completes.
• Enhances cask upgrades to deduplicate summary output and optionally record upgraded casks / reuse prefetched Cask::Installer instances; updates specs accordingly.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/upgrade.rb	Refactors dependent formula filtering, adds support for prefetched installers, and introduces deferred cleanup control during upgrades.
Library/Homebrew/cask/upgrade.rb	Adds deduped summaries plus plumbing to reuse prefetched cask installers and record upgraded casks.
Library/Homebrew/test/upgrade_spec.rb	Adds/adjusts tests for deferred cleanup and prefetched dependent installer behavior.
Library/Homebrew/test/cask/upgrade_spec.rb	Updates tests for new cask-upgrade behaviors and installer plumbing.

Suppressed comments (1)

Library/Homebrew/cask/upgrade.rb:284

• Matching a prefetched installer with installer.cask.equal?(new_cask) relies on object identity. If prefetched_cask_installers is provided by a caller (e.g. from an earlier planning/prefetch step), the Cask instances may not be the same object even when they represent the same token, causing the prefetched installer not to be reused and potentially re-downloading. Match on a stable identifier (e.g. full_name/token) instead.

      upgradable_casks.each_with_index do |(old_cask, new_cask), index|
        new_cask_installer = prefetched_cask_installers.find { |installer| installer.cask.equal?(new_cask) }
        upgrade_cask(

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