Make biopython an optional dependency

[IAlibay]

Fixes #3820

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

Developers certificate of origin

• I certify that this contribution is covered by the LGPLv2.1+ license as defined in our LICENSE and adheres to the Developer Certificate of Origin.

---

📚 Documentation preview 📚: https://mdanalysis--4332.org.readthedocs.build/en/4332/

[pep8speaks]

Hello @IAlibay! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file package/MDAnalysis/analysis/align.py:

Line 1180:1: W293 blank line contains whitespace

Comment last updated at 2023-11-07 09:18:44 UTC

[github-actions]

Linter Bot Results:

Hi @IAlibay! Thanks for making this PR. We linted your code and found the following:

Some issues were found with the formatting of your code.

Code Location	Outcome
main package	⚠️ Possible failure
testsuite	⚠️ Possible failure

Please have a look at the darker-main-code and darker-test-code steps here for more details: https://github.com/MDAnalysis/mdanalysis/actions/runs/6782384299/job/18434498431

---

Please note: The black linter is purely informational, you can safely ignore these outcomes if there are no flake8 failures!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (20013d8) 93.37% compared to head (ffa3a57) 93.36%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4332      +/-   ##
===========================================
- Coverage    93.37%   93.36%   -0.01%     
===========================================
  Files          170      184      +14     
  Lines        22309    23433    +1124     
  Branches      4076     4079       +3     
===========================================
+ Hits         20830    21879    +1049     
- Misses         962     1036      +74     
- Partials       517      518       +1     

Files	Coverage Δ
package/MDAnalysis/analysis/align.py	96.48% <100.00%> (+0.10%)	⬆️
package/MDAnalysis/core/topologyattrs.py	96.15% <100.00%> (+0.02%)	⬆️

... and 15 files with indirect coverage changes

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[RMeli]

I think this needs a changelog entry?

[RMeli]

Last nitpicks but LGTM

[RMeli]

/azp run Azure_Tests Linux-Python39-64bit-full-wheel

[azure-pipelines]

No pipelines are associated with this pull request.

[RMeli]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).