refactor: remove SlideBuilder.customize

[ya7010]

Summary

• remove the redundant SlideBuilder.customize API
• keep SlideBuilder.tap as the single callback escape hatch
• update slide tests to use tap only

Testing

• uv run ruff check src/tppt/pptx/slide.py tests/test_slide.py tests/test_table.py
• uv run pytest tests/test_slide.py tests/test_table.py -q

[Copilot]

Pull request overview

This PR removes the redundant SlideBuilder.tap API and standardizes slide customization on SlideBuilder.customize, updating related tests accordingly.

Changes:

• Removed SlideBuilder.tap from src/tppt/pptx/slide.py.
• Updated slide tests to validate customize() behavior (including raw python-pptx access).
• Deleted dead/unreachable tap-based table test code and simplified table imports.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/tppt/pptx/slide.py	Removes the tap builder API, leaving customize as the supported hook.
tests/test_slide.py	Migrates tap tests to customize and removes tap-specific coverage.
tests/test_table.py	Drops dead tap-based test code and trims unused imports.

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