extend/os/mac/system_config: check for Metal Toolchain

[p-linnane]

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Starting with Xcode 26 the Metal Toolchain is no longer bundled. We're starting to see formulae that depend on the presence of the Metal Toolchain. This PR adds a check to brew config to output if the toolchain is installed to help us verify inevitable reports. If we start identifying enough formulae we may want to add depends_on :metal_toolchain, but I don't think that's necessary yet.

[Copilot]

Pull Request Overview

This PR adds Metal Toolchain detection to brew config output. Starting with Xcode 26, the Metal Toolchain is no longer bundled and must be installed separately. This change helps diagnose issues with formulae that depend on the Metal Toolchain by showing its installation status in the configuration output.

Key Changes:

• Adds a metal_toolchain method that detects Metal Toolchain presence by running xcrun metal -v
• Displays Metal Toolchain status in brew config output when Xcode version is 26.0 or higher
• Uses proper Sorbet type signature for the new method

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[Copilot]

Pull Request Overview

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[MikeMcQuaid]

Makes sense, thanks!

[Copilot]

Pull request overview

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[Copilot]

Pull request overview

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

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