Rewrite the printer

[otherjoel]

Printer rewritten as a token-stream greedy layout. Fixes a bunch of niggling issues with the original printer:

• Off-by-one fixed: lines may fill the wrap width exactly
• Breaks allowed wherever the input has whitespace, including " " and "\n" strings
• Inline closing tags stay glued after trailing whitespace is hoisted
• Nested flow after text indents as a sibling; text after a closed block is indented
• Tag name and first attribute glued (<a href=)
• no trailing spaces on wrapped lines
• No whitespace-only lines (empty flow elements, trailing <br>, deep nesting)
• Whitespace containing newlines is collapsed, never written raw
• Prints </pre> closer at column 1 after content ending in a newline
• Empty blocks keep their closing tag glued to the opener

The new printer is about 2.3× faster on a 2 MB document.

The algorithm improvements and test additions were LLM-assisted.