Add padded bottle build prefixes

[MikeMcQuaid]

• Record padded-prefix eligibility in bottle tab metadata while formulae retain their tag-default cellars.
• Fetch tab metadata before rejecting a location-incompatible bottle and patch marked bottles from their literal built_prefix.
• Keep platform-specific padded bottles as separate tags instead of collapsing them into :all.

This change is part of plans/relocatable-bottles.md

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Codex with GPT 5.6-sol at Extra High effort, with local review and testing.

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[Copilot]

Pull request overview

Adds platform-specific padded bottle prefixes and metadata across Homebrew’s bottle creation, merging, and pouring pipeline.

Changes:

• Defines canonical 64-byte prefixes and records padded-prefix eligibility in bottle tabs.
• Uses bottle metadata to validate and relocate padded bottles.
• Prevents padded platform bottles from collapsing into :all bottles and adds coverage.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Library/Homebrew/global.rb	Defines padded prefix constants.
Library/Homebrew/utils/bottles.rb	Maps bottle tags to padded prefixes.
Library/Homebrew/tab/tab.rb	Serializes padded-prefix metadata.
Library/Homebrew/bottle_specification.rb	Checks padded bottle compatibility.
Library/Homebrew/bottle.rb	Applies tab metadata to bottle locations.
Library/Homebrew/formula_installer.rb	Fetches metadata and relocates padded bottles.
Library/Homebrew/dev-cmd/bottle.rb	Generates and merges padded bottle metadata.
Library/Homebrew/plans/relocatable-bottles.md	Updates the migration plan.
Library/Homebrew/test/utils/bottles/tag_spec.rb	Tests padded tag prefixes.
Library/Homebrew/test/tab_spec.rb	Tests metadata serialization.
Library/Homebrew/test/formula_installer_spec.rb	Tests padded bottle pouring.
Library/Homebrew/test/dev-cmd/bottle_spec.rb	Tests output and merge behavior.
Library/Homebrew/test/bottle_specification_spec.rb	Tests padded location compatibility.

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