fix: edge cases highlight codeblock

[urmauur]

Describe Your Changes

Enforce strict code block rules,

• The code block should start with triple backticks followed by a file extension (```css), and end with triple backticks (```).
  This ensures that the code block is correctly defined with both the opening and closing triple backticks, with an optional file extension immediately after the opening backticks.

• Multiple code blocks may impact each other. For example, if one of the code blocks is missing a formatting rule (e.g., missing the closing backticks), none of the code blocks will be highlighted

Fixes Issues

• Closes bug: Handle edge cases around syntax highlighting feature in input box #3884
• Closes #

Self Checklist

• Added relevant comments, esp in complex areas
• Updated docs (for bug fixes / features)
• Created issues for follow-up changes or refactoring needed

[github-actions]

Barecheck - Code coverage report

Total: 69.34%

Your code coverage diff: 0.04% ▴

Uncovered files and lines

File	Lines
web/screens/Thread/ThreadCenterPanel/ChatInput/RichTextEditor.tsx	96-97, 99, 119-120, 122, 143, 152, 155, 163, 165-168, 175, 180-181, 183, 185-186, 188, 190, 194, 209, 270, 273-274, 278, 289, 314-319, 336, 352, 358