feat/fix: Support for FixedSizeList vectors, nested schemas, and UI text wrapping

[mattiabonzi]

Description

This PR introduces several fixes for vector serialization and adds UI enhancements for viewing complex data structures. Specifically, it adds support for FixedSizeList vector types and improves the rendering of nested structs and lists. It also includes UI controls for text wrapping.

Bug Fixes (Commit: fix: Enhance serialization and vector handling)

• FixedSizeList Vector Support: Updated app.py to check for pa.types.is_fixed_size_list(). Previously, strictly typed vectors (which are required for LanceDB IVF_PQ indexes) were bypassed and fell back to raw text rendering. They now correctly trigger the vector preview/heatstrip UI.
• Null Scalar Crash: Added an is_valid check in serialize_value.py to prevent Cannot export buffer from null Arrow Scalar errors when encountering empty cells.
• StructScalar & StringScalar Extraction: Fixed extraction methods in PyArrow serialization to prevent StructScalar has no attribute 'field' errors, and refined the binary check so standard text strings (StringScalar) aren't accidentally Base64 encoded.

New Features

1. Nested Schemas & Complex Objects (Commit: feat: manage nested vectors and complex objects in the UI)

• Recursive Backend Serialization: app.py now recursively walks through PyArrow Structs and Lists, allowing it to detect and format vectors even when they are deeply nested inside complex objects.
• Interactive UI Builder: Replaced the default [object Object] JavaScript rendering with a clean, recursive DOM builder in app.js. Complex structs and arrays now render as neatly indented, syntax-highlighted blocks.
• Smart Collapsing: Arrays and objects with more than 5 items are now collapsed by default, featuring a "Show X more..." toggle to prevent massive payload boxes from breaking the table layout.
• Clean CSS Integration: Added all corresponding styles to styles.css (.complex-object-wrapper, .co-list, etc.) keeping the JS DOM construction clean of inline styles.

2. Dynamic Text Wrapping (Commit: feat: add text wrapping)

• Wrap Text Toggle: Added a "Wrap Text" checkbox to the dataset header next to the pagination controls.
• Dynamic Table Styling: Toggling the checkbox applies a .wrap-text class to the data table, limiting cell width to 600px and enforcing break-word wrapping. This allows users to instantly switch between a compact "spreadsheet" view and a readable "document" view for long text fields.

Testing

• Verified against standard scalar columns, FixedSizeList<Float32> vectors, and complex nested schemas (e.g., lists of structs containing vectors).
• Tested UI toggles (Show more/less, Wrap Text) for responsive DOM updating.
• Rebuilt and tested successfully for version 0.24.3.

Screenshot

[gordonmurray]

Hey @mattiabonzi thanks for this PR, really nice work. The FixedSizeList fix is a genuine gap in the current code, the null scalar handling prevents real crashes, and the nested object renderer is a great addition.

All 10 CI checks passed, but the PR now has merge conflicts against main (likely from the serialize_value refactor that landed in #9). Would you be able to rebase onto the latest main?

While you're in there, a small thing I noticed Inline styles in index.html, the flex container around the Wrap Text checkbox uses inline style= attributes. Could you move those to named classes in styles.css? The project keeps styles out of the HTML.

The actual functionality looks good. Happy to merge once the conflicts are resolved. Thanks again for taking the time on this!