add support for tab-bar mode (#21)

[Artawower]

This PR adds optional tab-bar/tabspaces-aware zoom state isolation.

When zoom-window-use-tab-bar is non-nil, zoom-window stores zoom state per tab-bar tab instead of sharing it across the whole frame. This makes zoom/unzoom
work correctly with tab-bar-based workflows, including tabspaces, where each tab should keep its own zoomed window state. It should solve the issue #21

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds optional tab-bar/tabspaces-aware zoom state isolation so zoom/unzoom state is tracked per tab instead of per frame when enabled.

Changes:

• Introduces zoom-window-use-tab-bar defcustom and tab-bar state helpers to persist per-tab zoom data.
• Updates setup + save/restore paths to use per-tab state when tab-bar mode is enabled.
• Adds ERT coverage for tab-bar behavior and idempotent setup.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
zoom-window.el	Adds tab-bar-aware state storage and integrates it into setup and zoom state save/restore.
test/zoom-window-tab-bar-test.el	Adds ERT tests validating per-tab isolation and setup hook idempotence.

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