[FIX] Handle nested comment markers in multiline comments

[Mirochill]

Reference Issue

Fixes #174

What does this implement/fix? Explain your changes.

• Tracks the current block-comment indentation while replacing internal [CI] newline markers.
• Handles the reproducer where a -- line appears inside a /* ... */ block without requiring every [CI] marker to be on the same line as the opening /*.
• Adds notebook regression coverage for that multiline comment pattern.

Any other comments?

Validation:

• git diff --check
• git diff --check HEAD~1..HEAD
• Parsed nbs/00_core.ipynb and nbs/99_additional_tests.ipynb as JSON
• Not run locally