refactor(chart-render): use typed pptx access wrappers for chart ops

[tmustier]

Summary

Continue the dynamic-access cleanup by moving remaining chart-render runtime probes into pptx_access helpers and updating chart_render.py to consume those typed wrappers.

Changes

Shared helper expansions (clean_slides/pptx_access.py)

Added wrappers for chart-render paths that previously relied on Any and direct dynamic attribute chains:

• chart XML and chart insertion
  • chart_xml_element(...)
  • slide_add_chart(...)
• chart/plot mutation
  • set_chart_has_legend(...)
  • chart_series(...)
  • chart_plots(...)
  • chart_first_plot(...)
  • set_plot_has_data_labels(...)
  • plot_data_labels(...)
• series/point styling helpers
  • series_points(...)
  • point_fill_solid(...)
  • point_fill_fore_color(...)
  • point_line_fill_background(...)
• slide/page helpers
  • slide_size_emu(...)
• text helpers
  • paragraph_font(...)
  • set_font_size(...)

chart_render.py migration

• Removed Any-based chart handling in this module for chart insertion/mutation paths.
• Replaced:
  • cast(Any, slide.shapes).add_chart(...) with slide_add_chart(...)
  • chart_frame.chart access with shape_chart(...)
  • chart.has_legend = ... with set_chart_has_legend(...)
  • chart.plots[0] + direct data-label access with chart_first_plot(...), set_plot_has_data_labels(...), plot_data_labels(...)
  • direct _element access with chart_xml_element(...) in label/title XML edits
  • direct point formatting chains with point helpers
  • slide.part.package...presentation... chain with slide_size_emu(...)
  • paragraph font getattr(...) access with paragraph_font(...) + set_font_size(...)
• Added local XML protocols for minimal typed OOXML traversal (_XmlElementLike, _XmlSettable).

Tests

• Expanded tests/test_pptx_access.py with dedicated coverage for all newly introduced chart mutation/slide access helpers:
  • adding chart through slide helper
  • chart legend mutation
  • chart xml extraction
  • plot/data-label mutation
  • series/point helper behavior
  • slide size extraction
  • paragraph font size mutation

Validation

• .venv/bin/ruff check clean_slides tests
• .venv/bin/pyright
• .venv/bin/pytest -q
• .venv/bin/pre-commit run --all-files

All green locally.