Bug 1: Inline code after list bullets not detected
- After emitting a list bullet, at_line_start was not set to false
- This caused the next backtick to be treated as a potential code fence
- Fixed by setting at_line_start = false after emitting bullet
Bug 2: Code block closing on indented backticks
- Code blocks containing indented ``` (4+ spaces) were closing prematurely
- The .trim() check was too permissive
- Fixed by only allowing closing fence with <= 3 spaces indent (CommonMark spec)
Added tests for both edge cases.