fix(examples): resolve all mypy type errors #2047

[joelpaulfernandez]

Summary

Fixes #2047.

Resolves all mypy errors in py/examples/ (209 → 0) without breaking existing functionality.

• Add py/mypy.ini with disable_error_code = import-untyped for third-party packages lacking py.typed markers, and ignore_missing_imports for synth, h2o, altair, vega_datasets, plotly
• Add pandas-stubs to requirements.txt for real pandas type checking instead of suppression
• Relax pinned versions to >= in requirements.txt for Python 3.13 compatibility
• Use Optional[T] for parameters that default to None (synth.py, table_pagination.py, table_pagination_pandas.py)
• Switch to import h2o_wave.graphics as g in 8 graphics files — mypy 1.19 no longer resolves the submodule via __init__.py re-export
• Replace deprecated pd.np with numpy directly (table_markdown_pandas.py)
• Wrap bokeh.embed.json_item() second argument with ID() cast (plot_bokeh_*.py)
• Add # type: ignore[attr-defined] for bokeh js_on_change dynamic attribute
• Update tour.py type: ignore comment to cover str-unpack error code (mypy 1.19)
• Fix pu(1) → pu(close=True) in graphics_turtle.py, graphics_background.py
• Fix update_ui value parameter type int → float (background_progress.py)
• Guard against None rows in db_todo.py list comprehension
• Replace builtin any with Any from typing (plot_events_routing.py)
• Rename shadowed loop variable filters → col_filters (table_pagination.py)

Test plan

• mypy py/examples/ reports 0 errors
• Static examples render correctly (splines, bokeh, turtle/spirograph)
• Table pagination loads and page navigation works