csv_preview: Add row filtering feature

[HalavicH]

Objective

CSV feature needs row filtering feature by column values. This PR provides base implementation of it with barebones ui.

NOTE: Sleek UI with search & proper scrolling hanling is implemented in next PR. It's stacked on top to reduce review scope

Solution

• New FilterEntry / FilterEntryState model in table_data_engine/filtering_by_column.rs tracking per-column applied/candidate filter values
• Filtering runs in the background (feat: Implement background filtering) so large CSVs don't block the UI thread while a filter is applied
• Filter menu entries reflect live counts and support a configurable sort order (FilterSortOrder, added in renderer/settings.rs / settings.rs)
• Filter/sort trigger buttons on column headers are hidden until hover, using GradientFade (new in ui/src/components/gradient_fade.rs) to fade content behind them

Testing

Filter chain tested on csv fixtures with multiple filters applied sequentially columns.

Self-Review Checklist: (todo)

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content adheres to Zed's UI standards (UX/UI and icon guidelines)
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Showcase

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Release Notes:

• Added initial row filtering UI & logic