bundle: fix flaky installer spec

[MikeMcQuaid]

• keep cached Cask and tap state from leaking between examples
• exercise Installer.reset! instead of poking cached internals
• stub parallel formula metadata in installer_spec.rb

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[Copilot]

Pull request overview

This PR improves brew bundle test isolation by adding an Installer.reset! entrypoint and updating installer_spec.rb to use it, preventing cached Bundle/Cask/Tap state from leaking between RSpec examples.

Changes:

• Add Homebrew::Bundle::Installer.reset! to clear cached state prior to installs.
• Update installer_spec.rb to call Installer.reset! in before hooks and add a regression spec for stale cached cask state.
• Stub additional formula metadata methods used by parallel installation dependency/lock analysis.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
Library/Homebrew/test/bundle/installer_spec.rb	Resets installer state between examples and extends stubbing to cover parallel installer dependency metadata.
Library/Homebrew/bundle/installer.rb	Introduces Installer.reset! to clear cached Bundle/Cask/Tap state.

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