Add debug e2e harness and export debug metadata for Myslot import/export flow

[Copilot]

Implemented a debug-only e2e path to launch WoW UI, click Export/Import, and validate addon flow via the existing /myslot command, and added debug metadata stamping to exported text.

• Test hooks: Expose import/export buttons and edit box through MySlot.TestHooks, including dialog identifier, e2e runner, and export debug hook.
• Debug e2e script: wowtest/myslot-e2e.lua runs export → import automatically, accepts the confirmation popup, and contributes debug metadata; triggered with /myslot e2e.
• Export debug metadata: Export output now prepends optional debug lines supplied by MySlot.TestHooks.exportDebugInfo, with safe handling for hook errors and non-string entries.
• Packaging: Include the e2e script in the debug section of Myslot.toc; allow luacheck to recognize the entry points.

Example usage:

-- In WoW client debug build
/myslot e2e  -- opens Myslot, exports current layout, imports it back, confirms dialog, stamps debug metadata

Original prompt

impl e2e test, start wow.exe and test the addon, click import and export button

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