refactor(config): pull out shared default keymaps

[dlyongemallo]

No description provided.

[Copilot]

Pull request overview

This PR refactors diffview.config’s default keymap definitions by extracting shared mappings into common tables and composing per-section keymap lists from those shared defaults. It also adds functional tests to ensure shared and section-specific mappings are present (and don’t leak across sections).

Changes:

• Added common_nav_keymaps and common_panel_keymaps and used a composition helper to build view, file_panel, and file_history_panel defaults.
• Updated view defaults to include actions.compat.fold_cmds via composition rather than unpack().
• Added functional tests validating shared/section-specific keymaps distribution across sections.

Reviewed changes

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

File	Description
lua/diffview/config.lua	Extracts shared default keymaps into common lists and composes section keymaps from them.
lua/diffview/tests/functional/config_spec.lua	Adds functional tests asserting shared keymaps exist in expected sections and section-only mappings don’t leak.

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