Add wrapped lines option to diff views

[atacan]

Summary

Adds an opt-in wrapped lines mode to JSDiffUI so long diff lines wrap onto multiple visual rows (with a ↪ continuation marker) instead of being truncated or overflowing.

Changes

• DiffStyle: new wrapLongLines: Bool = false and wrapMarker: String = "↪ " options, plus a withWrapLongLines(_:marker:) builder method
• DiffLineWrapper (new): word-boundary chunking engine — hard-splits words longer than the limit, consumes break spaces, and accounts for marker width on continuation rows. Also includes DiffMetrics for estimating characters-per-line from available width using platform monospaced fonts (UIKit/AppKit)
• DiffWrappedContentView (new): shared view rendering a line as stacked visual rows; continuation rows get the marker, dimmed text, the same background highlight, and blank line-number gutters so alignment is preserved
• Views: UnifiedDiffView, UnifiedPatchView, InlineDiffLineView, and side-by-side columns measure their own width via GeometryReader and thread the wrap limit down
• API: .wrapLines(_:) / .wrapLines(_:marker:) modifiers on DiffView, PatchView, and PatchesView
• Tests: 6 unit tests covering short text, word-boundary breaks, hard splits, marker capacity accounting, empty input, and tiny limits
• README documentation + wrapped-lines SwiftUI preview

Default behavior is unchanged (wrapLongLines defaults to false).

Usage

DiffView(changes: changes, displayStyle: .unified)
    .wrapLines(true)

// Custom continuation marker
DiffView(changes: changes)
    .wrapLines(true, marker: "… ")

Implementation note

SwiftUI's AttributedString doesn't support paragraph-level hanging indents, so wrapping is done by pre-splitting into estimated-width segments rather than relying on native text layout. A TextKit-based implementation could replace the estimator later for pixel-perfect wrapping.

Testing

• swift build ✅
• swift test — all 32 tests pass (including 6 new wrapper tests) ✅