pathname: eagerly initialize lazy instance variables

[p-linnane]

Continues d57efd9 by initialising the lazy memoised instance variables defined in extend/pathname.rb and DiskUsageExtension (@magic_number, @file_type, @zipinfo, @which_install_info, @disk_usage, @file_count) up front via a new EagerInitializeExtension module that's prepended at class-body time (same shape as the precedent in extend/os/mac/unpack_strategy/zip.rb).

Every Pathname instance now shares the same object shape regardless of which lazy method is hit first, so we no longer see:

warning: The class Pathname reached 8 shape variations, instance variables accesses will be slower and memory usage increased.
It is recommended to define instance variables in a consistent order, for instance by eagerly defining them all in the #initialize method.

Verified locally: 50 Pathname instances exercising the lazy methods in varied orders all collapse to a single ObjectSpace.dump shape (vs 8+ before). A pathname_spec.rb example asserts every lazy ivar is defined and nil immediately after Pathname.new so future regressions are caught in CI.

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Claude Code (Opus 4.7) located the remaining lazy ivars, drafted the prepended initializer module, and ran the verification steps. Manually reviewed the diff against the conventions in extend/pathname/ (file layout, naming, requires_ancestor, sig style) and the prepend precedent in extend/os/mac/unpack_strategy/zip.rb; ran brew lgtm locally; confirmed the warning no longer reproduces and that ObjectSpace.dump collapses to a single shape across 50 instances exercising the lazy methods in varied orders.

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[Copilot]

Pull request overview

This PR addresses Ruby “object shape variation” warnings for Pathname by eagerly defining previously-lazy memoized instance variables up front, ensuring all Pathname instances share a consistent instance-variable layout regardless of which memoized method is called first.

Changes:

• Add a new EagerInitializeExtension module that defines the relevant memoized ivars in initialize.
• Require and prepend the new extension into Pathname so initialization happens for all instances.

Reviewed changes

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

File	Description
Library/Homebrew/extend/pathname/eager_initialize_extension.rb	New prepended extension to eagerly initialize previously-lazy Pathname/DiskUsageExtension ivars.
Library/Homebrew/extend/pathname.rb	Requires the new extension and prepends it into Pathname at class-body time.

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[MikeMcQuaid]

Thanks! One comment and then can self-merge without rereview.