Improve Linux cask handling

[MikeMcQuaid]

• Avoid requiring --cask and implicitly adding --formula on Linux
• Fix some hardcoded system utility paths and system groups that don't apply on Linux

Fixes #20916

[Copilot]

Pull Request Overview

This PR improves cask handling on Linux by removing platform-specific command-line parsing behavior and fixing hardcoded system utility paths. The changes ensure casks work more naturally on Linux without requiring special flags and make system commands portable across platforms.

• Removes Linux-specific CLI parser that auto-enabled --formula flag
• Replaces hardcoded macOS system utility paths (/bin/chmod, /usr/sbin/chown, etc.) with plain command names
• Adds Linux-specific override for caskroom group ownership (using root instead of admin)

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Library/Homebrew/cli/parser.rb	Removes require for OS-specific parser extensions
Library/Homebrew/extend/os/parser.rb	File deleted - no longer needed
Library/Homebrew/extend/os/linux/cli/parser.rb	File deleted - removes auto---formula behavior on Linux
Library/Homebrew/test/cli/parser_spec.rb	Updates test expectations to reflect that --formula is no longer set by default
Library/Homebrew/cask/caskroom.rb	Extracts group change logic to allow OS-specific overrides; removes hardcoded paths
Library/Homebrew/extend/os/cask/caskroom.rb	New file to load Linux-specific caskroom extensions
Library/Homebrew/extend/os/linux/cask/caskroom.rb	New file providing Linux override for group ownership (uses root instead of admin)
Library/Homebrew/cask/staged.rb	Removes hardcoded paths for chmod and chown
Library/Homebrew/cask/utils.rb	Removes hardcoded paths for mkdir, rmdir, chmod, and chown
Library/Homebrew/cask/utils/rmdir.sh	Removes hardcoded paths for rmdir and test
Library/Homebrew/cask/quarantine.rb	Removes hardcoded path for chmod
Library/Homebrew/cask/artifact/relocated.rb	Removes hardcoded path for chmod
Library/Homebrew/cask/artifact/binary.rb	Removes hardcoded path for chmod
Library/Homebrew/test/cask/dsl/shared_examples/staged.rb	Updates test expectations to use plain command names instead of hardcoded paths

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