Describe your changes

Modernizes st.pydeck_chart width parameter to use the new Width type system ("stretch" or pixel values) and deprecates the use_container_width parameter for consistency with other chart elements.

This PR also begins the process of deprecating use_container_width. The default is updated to None, and width will be used instead. If the user explicitly passes a value for use_container_width then that will take precedence. use_container_width=True is equivalent to width="stretch" and setting the width to an integer can be done without setting use_container_width. The user will be given a warning and suggestion to use width instead. We will remove use_container_width after 12-31-2025.

Changes Made:

• Updated parameter signature: Changed width: int | None = None to width: WidthWithoutContent = "stretch"
• Deprecated use_container_width: Changed from bool = True to bool | None = None with deprecation warnings
• Preserved backward compatibility: Existing integer width values and use_container_width behavior still work
• Updated layout system: Uses LayoutConfig(width=width) instead of direct proto field assignment
• Enhanced parameter validation: Validates width parameter with appropriate error messages

Key Implementation Details:

Width Parameter Modernization:

• Breaking change: Default changes from width=None to width="stretch"
• Intelligent fallback: When use_container_width=False, preserves existing integer width values instead of converting to "content"

Backward Compatibility & Deprecation:

Deprecation Timeline: use_container_width will be removed after 12-31-2025.

Parameter Precedence: If user explicitly passes use_container_width, it takes precedence over width:

• use_container_width=True → width="stretch" (overrides width parameter)
• use_container_width=False → width="content" (overrides width parameter)

Intelligent Fallback: When use_container_width=False with existing integer widths:

• use_container_width=False + width=400 → width=400 (preserves integer)
• use_container_width=False + width="content" → width="content"
• use_container_width=False + width="stretch" → width="content" (fallback)

User Experience: Users receive deprecation warnings with suggestions to use width parameter instead.

GitHub Issue Link (if applicable)

Testing Plan

• Unit Tests (Python) - New width parameter functionality
• Unit Tests (Python) - use_container_width backward compatibility with deprecation warnings
• Unit Tests (Python) - Native chart width extraction
• E2E Tests - Visual width behavior across different values (width="content", width="stretch", width=400)
• Manual testing completed for all width scenarios

Additional Notes:
This follows the established pattern from st.vega_lite_chart, st.line_chart, and st.plotly_chart. Part of the broader AdvancedLayouts initiative to provide consistent width APIs across all chart elements.

Contribution License Agreement

By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.