docs: update conf.py to be in sync with mesa

[wang-boyu]

RTD is failing due to an error:

ERROR: Invalid value `None` in intersphinx_mapping['http://docs.python.org/']. Expected a two-element tuple or list.

Fixing as in projectmesa/mesa#2206

Also updating some settings to be the same as Mesa

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.30%. Comparing base (ce501b6) to head (6508e31).
Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #223      +/-   ##
==========================================
+ Coverage   78.21%   78.30%   +0.08%     
==========================================
  Files          10        9       -1     
  Lines         693      765      +72     
  Branches      151      173      +22     
==========================================
+ Hits          542      599      +57     
- Misses        127      131       +4     
- Partials       24       35      +11     

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[EwoutH]

Looks good!