fix(inline): stack tree-sitter captures so @spell doesn't drop @comment's fg

[dlyongemallo]

Relates to #156 (comment).

[Copilot]

Pull request overview

This PR updates Diffview’s inline deletion rendering to keep Tree-sitter highlight attributes composable when multiple captures overlap (notably ensuring decoration-only captures like @spell don’t clobber earlier captures’ foreground like @comment). This fits into the inline diff rendering path by improving how virt_line highlight group stacks are constructed for deleted text.

Changes:

• Change captured_chunks to preserve the full per-byte capture stack (instead of reducing to a single “latest” capture).
• Coalesce runs by comparing stacked capture lists, and forward { del_hl, cap1, cap2, ... } to let Neovim merge attributes correctly.
• Extend functional tests to cover overlapping capture stacking and the @comment + @spell regression scenario.

Reviewed changes

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

File	Description
lua/diffview/scene/inline_diff.lua	Reworks captured_chunks to build/compare per-byte capture stacks and forward the full hl-group list for correct attribute composition.
lua/diffview/tests/functional/inline_diff_spec.lua	Updates/extends tests to assert stacked capture behavior, including @spell not dropping @comment fg.

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