fix(panel): skip batch_selection notification when nothing changed

[dlyongemallo]

No description provided.

[Copilot]

Pull request overview

This PR updates Diffview’s diff file panel selection batching so that batch_selection() only emits a selection-changed notification when the batch actually performed (or attempted) a notification-worthy mutation, avoiding no-op notifications.

Changes:

• Update FilePanel:batch_selection() / _notify_selection_changed() to coalesce multiple selection mutations into a single notification and skip notifying on an empty batch.
• Add functional tests verifying batch_selection() notifies once for multiple mutations and not at all when nothing changes.

Reviewed changes

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

File	Description
lua/diffview/scene/views/diff/file_panel.lua	Adjusts batching/notification logic to avoid no-op batch_selection() notifications.
lua/diffview/tests/functional/selection_store_spec.lua	Adds functional coverage for the updated batch_selection() notification behavior.

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