refactor(panel): pull out some repeated code into their own functions

[dlyongemallo]

No description provided.

[Copilot]

Pull request overview

This PR refactors Diffview’s panel implementations to reduce duplicated logic by extracting repeated keymap-application and file-component construction code into reusable helpers.

Changes:

• Added Panel:apply_keymaps() to centralize applying configured buffer-local keymaps (with merged default options).
• Refactored FilePanel:update_components() to use small helpers for list/tree component schema construction.
• Added functional tests covering FilePanel:update_components() behavior (list/tree) and Panel:apply_keymaps() option-merging behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
lua/diffview/ui/panel.lua	Adds Panel:apply_keymaps() helper to apply keymaps from config sections with merged defaults.
lua/diffview/scene/views/file_history/option_panel.lua	Replaces inline keymap loop with self:apply_keymaps("option_panel").
lua/diffview/scene/views/file_history/file_history_panel.lua	Uses apply_keymaps() and reuses returned config for find_*_keymap lookups.
lua/diffview/scene/views/diff/file_panel.lua	Uses apply_keymaps() and extracts list/tree component-building into local helpers.
lua/diffview/tests/functional/panel_spec.lua	Adds functional tests for FilePanel:update_components() and Panel:apply_keymaps().

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