data_table: Rework column/table width API

[HalavicH]

data_table: Replace column width builder API with ColumnWidthConfig enum

This PR consolidates the data table width configuration API from three separate builder methods (.column_widths(), .resizable_columns(), .width()) into a single .width_config(ColumnWidthConfig) call. This makes invalid state combinations unrepresentable and clarifies the two distinct width management modes.

What changed:

• Introduces ColumnWidthConfig enum with two variants:
  • Static: Fixed column widths, no resize handles
  • Redistributable: Drag-to-resize columns that redistribute space within a fixed table width
• Introduces TableResizeBehavior enum (None, Resizable, MinSize(f32)) for per-column resize policy
• Renames TableColumnWidths → RedistributableColumnsState to better reflect its purpose
• Extracts all width management logic into a new width_management.rs module
• Updates all callers: csv_preview, git_graph, keymap_editor, edit_prediction_context_view

pub enum ColumnWidthConfig {
    /// Static column widths (no resize handles).
    Static {
        widths: StaticColumnWidths,
        /// Controls widths of the whole table.
        table_width: Option<DefiniteLength>,
    },
    /// Redistributable columns — dragging redistributes the fixed available space
    /// among columns without changing the overall table width.
    Redistributable {
        entity: Entity<RedistributableColumnsState>,
        table_width: Option<DefiniteLength>,
    },
}

Why:

The old API allowed callers to combine methods incorrectly. The new enum-based design enforces correct usage at compile time and provides a clearer path for adding independently resizable columns in PR #3.

Context:

This is part 2 of a 3-PR series improving data table column width handling:

1. #51059 - Extract modules into separate files (mechanical change)
2. This PR: Introduce width config enum for redistributable column widths (API rework)
3. Implement independently resizable column widths (new feature)

The series builds on previously merged infrastructure:

• #46341 - Data table dynamic column support
• #46190 - Variable row height mode for data tables

Primary beneficiary: CSV preview feature (#48207)

Anthony's note

This PR also fixes the table dividers being a couple pixels off, and the csv preview from having double line rendering for a single column in some cases.

Before you mark this PR as ready for review, make sure that you have:

• Added a solid test coverage and/or screenshots from doing manual testing
• Done a self-review taking into account security and performance aspects
• Aligned any UI changes with the UI checklist

Release Notes:

• N/A

[Anthony-Eid]

If we end up splitting up some of data_table.rs into width_managements.rs that should be it's own PR, just to make this one as easy to review as possible.

[Anthony-Eid]

I would rather prevent separating data_table.rs into two files, it's inconsistent with the rest of the Zed codebase for the most part, and it would make finding the resizable columns stuff harder for devs that are used to our current organization patterns

[HalavicH]

Okay i'll merge it back in

[Anthony-Eid]

What's the motivation behind this change? Cargo.toml changes like this should be in their own PR

[HalavicH]

it seems i accidentally commited redundant commit

[HalavicH]

Does anything besides conflicts prevent this pr from being merged?

[Anthony-Eid]

Does anything besides conflicts prevent this pr from being merged?

There were some bugs with this PR that I just fixed. The resize behavior didn't work and all tables became resizable instead of being explicitly marked with the intractable function like it was before.

I also fixed the pixel mis alignment issues with the dividers for columns.