Fixes code samples in Sphinx docs that should have border

[swahtz]

This pull request updates the docstrings in the fvdb/jagged_tensor.py file to improve the formatting and clarity of example code blocks. The changes ensure consistent usage of reStructuredText (reST) code block directives, add missing code block formatting, and clarify example outputs by commenting them out. No functional code changes were made.

Documentation formatting improvements:

• Replaced incorrect or inconsistent code block directives (such as ... code-block:: python) with the correct .. code-block:: python in all relevant docstrings. [1] [2] [3] [4] [5] [6] [7] [8] [9]
• Added missing .. code-block:: python or .. code-block:: text directives to several example sections for better rendering in documentation tools. [1] [2] [3] [4] [5] [6] [7]
• Updated example outputs in code blocks to be comments (using #) instead of uncommented lines, clarifying that these lines are not executable code. [1] [2] [3] [4]
• Improved clarity in example outputs and argument documentation, such as using double backticks for inline code and clarifying which APIs to use for certain operations.
• Removed unnecessary blank lines and fixed indentation in several docstring examples for consistency. [1] [2]

Fixes #304