Misc improvements to the fast renderer

[krissetto]

Includes fixes for various rendering issues, along with improvements to general styling of certain elements to improve legibility in the TUI.

Here's a non-exhaustive list of the rendering improvements:

• more consistent spacing in general
• heading styles are more consistent, and compatible with italics, code blocks, strike-through, etc.
• word wrapping lines
• styling after an inline code block
• table styling
• things we previously didn't render like nested blockquotes
• code blocks in lists are correctly indented
• ordered/unordered lists have the same styling
• etc... see the videos 👇

After these changes, rendering performance improves slightly (in both speed and memory) for everything (currently benchmarked) except tables, which show a small regression due to the styling fixes. They should be meaningless in real-worlds scenarios.

Currently tested on Linux with ghostty and ptyxis, and MacOS using Ghostty, iTerm2 and the built-in Terminal

Screencasts

before

Screencast.From.2026-01-25.16-23-23.mp4

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after

Screencast.From.2026-01-25.19-24-54.mp4

[krissetto]

Also did some testing on MacOS using Ghostty, iTerm2 and the built-in Terminal