refactor(layouts): dedupe *Pinned overrides via shared_symbols

[dlyongemallo]

No description provided.

[Copilot]

Pull request overview

This PR refactors pinned layout swap behavior so shared/pinned window detachment is handled by the base Layout:detach_files_for_swap implementation instead of duplicated per pinned layout.

Changes:

• Centralizes shared-symbol detach logic in lua/diffview/scene/layout.lua.
• Removes duplicated detach_files_for_swap overrides from pinned Diff1/Diff2 layouts.
• Reuses the horizontal pinned Diff2 should_null implementation for the vertical pinned variant.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
lua/diffview/scene/layout.lua	Implements shared-symbol-aware swap detachment generically.
lua/diffview/scene/layouts/diff_1_pinned.lua	Removes now-redundant pinned detach override.
lua/diffview/scene/layouts/diff_1_inline_pinned.lua	Relies on base shared-symbol detach behavior and updates comments.
lua/diffview/scene/layouts/diff_2_hor_pinned.lua	Removes duplicated detach override and updates documentation.
lua/diffview/scene/layouts/diff_2_ver_pinned.lua	Aliases shared should_null logic from horizontal pinned layout.

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