feat: Return structured result with content/dimensions (no SVG wrapper)

[davefowler]

Summary

Add an option to return rendered content without the SVG wrapper, along with dimensions. This allows callers to compose multiple mdsvg outputs into a larger SVG without regex-stripping wrappers.

Use Case

When embedding mdsvg output in larger SVG compositions, callers need to:

1. Extract the inner content (currently requires regex)
2. Know the actual rendered dimensions

Current workaround:

# Hacky regex extraction in dataface
content_svg = mdsvg.render(markdown, width=400)
inner_match = re.search(r"<svg[^>]*>(.*)</svg>", content_svg, re.DOTALL)
markdown_content = inner_match.group(1)

# Also need to extract height via regex
height_match = re.search(r'height="([0-9.]+)"', content_svg)
height = float(height_match.group(1))

Proposed API

Option A: Structured result type

from mdsvg import render_content, RenderResult

result: RenderResult = render_content("# Hello", width=400)
result.content  # SVG elements without <svg> wrapper
result.width    # 400.0
result.height   # Actual rendered height
result.to_svg() # Full SVG with wrapper (convenience method)

Option B: Parameter to skip wrapper

# Returns just the inner content
content = render("# Hello", width=400, wrap=False)

# Separate function to get dimensions
dims = get_dimensions("# Hello", width=400)
dims.width, dims.height

Recommendation

Option A (structured result) is cleaner - it's the pattern we just implemented in dataface's LayoutResult and works well.

@cursor Instructions

1. Create a RenderResult dataclass with content, width, height fields
2. Add to_svg() method that wraps content in SVG element
3. Add render_content() function that returns RenderResult
4. Keep existing render() function unchanged for backward compatibility
5. Add tests for the new API
6. Update README with examples

[davefowler]

@cursor please implement this feature. Create the RenderResult dataclass first, then add the render_content() function.

[cursor]

I've implemented the feature as requested. Here's what was done:

Added RenderResult dataclass with:

• content: SVG elements without the <svg> wrapper (includes style block)
• width: Width of the rendered content
• height: Actual rendered height
• to_svg(): Convenience method to wrap content in a complete SVG element

Added render_content() function that returns a RenderResult instead of a string, enabling:

• Easy access to dimensions without regex parsing
• Composing multiple mdsvg outputs into larger SVGs
• Backward compatibility (existing render() function unchanged)

Tests added - 11 new tests covering:

• Return type validation
• Content structure (no SVG wrapper)
• Dimension accuracy
• to_svg() method
• Composability
• Custom styles
• Edge cases (empty input)

README updated with documentation and examples showing the new API usage.

All 134 tests pass, linting passes, and type checking passes.