fix(inline): guard async render against teardown and swap races

[dlyongemallo]

No description provided.

[Copilot]

Pull request overview

This PR hardens the diff1_inline layout’s async inline-render pipeline against races caused by entry swaps (use_entry) and teardown (teardown_render/destroy). It introduces a monotonic “render generation” token that invalidates in-flight async work, preventing stale callbacks from overwriting caches or rendering extmarks onto buffers after the layout no longer owns them.

Changes:

• Add _render_generation tokening plus _is_active_render() guards around async yield points in create, use_entry, _prerender, and _render_inline.
• Bump generation on lifecycle transitions (create, use_entry, teardown_render) so stale async resumes bail out safely.
• Add functional tests covering mid-flight generation changes, destroy/teardown during awaits, and cached-instance reuse after destroy.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lua/diffview/scene/layouts/diff_1_inline.lua	Introduces generation-based invalidation to prevent stale async renders from mutating state or leaking extmarks after swaps/teardown.
lua/diffview/tests/functional/layouts_spec.lua	Adds regression tests exercising swap/teardown/destroy race scenarios and cached layout reuse.

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