Suggestion for nbsphinx_execute Setting & Remove Redundant html_sourcelink_suffix

[SophiaLi20]

In doc/conf.py,

• Currently, nbsphinx_execute = "never" is used to disable notebook execution,
  but the recommended approach is to use "off" for better clarity and compatibility with newer Sphinx versions.

• Remove Redundant html_sourcelink_suffix:
  The setting html_sourcelink_suffix = "" is no longer needed, as modern Sphinx versions handle it automatically.

Suggested Fix:
Remove:
html_sourcelink_suffix = ""

Advantage:

• Ensures correct disabling of Jupyter notebook execution.
• Cleans up unnecessary settings, improving maintainability.