Fix Session.peer type annotation

[cuu508]

What do these changes do?

Updates the type annotation for the Session.peer field.

The annotation was "str or None".

I think the correct annotation should be "tuple[str, int] or None" (more in #518)

Are there changes in behavior for the user?

Type annotation changes should not affect code at runtime.

Dependent code could see new mypy warnings if it also uses the old, now incompatible, type annotation.

Related issue number

Fixes: #518

Checklist

• I think the code is well written
• Unit tests for the changes exist
• tox testenvs have been executed in the following environments:
  • Linux (Ubuntu 24.04) {py312}
  • Windows (7, 10): {py36,py37,py38,py39}-{nocov,cov,diffcov}
  • WSL 1.0 (Ubuntu 18.04): {py36,py37,py38,py39}-{nocov,cov,diffcov}, pypy3-{nocov,cov}, qa, docs
  • FreeBSD (12.2, 12.1, 11.4): {py36,pypy3}-{nocov,cov,diffcov}, qa
  • Cygwin: py36-{nocov,cov,diffcov}, qa, docs
• Documentation reflects the changes
• Add a news fragment into the NEWS.rst file

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.77%. Comparing base (f40ac96) to head (91d108b).
Report is 37 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #522      +/-   ##
==========================================
- Coverage   97.86%   97.77%   -0.10%     
==========================================
  Files          23       23              
  Lines        5707     5699       -8     
  Branches      764      764              
==========================================
- Hits         5585     5572      -13     
- Misses         76       82       +6     
+ Partials       46       45       -1     

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