Add support for type parameter defaults + string repr improvements

[cdce8p]

Description

Type parameter defaults were added in Python 3.13.
Also improved the string representation of various TypeVar / type param related nodes.

https://peps.python.org/pep-0696
https://peps.python.org/pep-0695

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.30%. Comparing base (4364218) to head (db0f2b7).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2797   +/-   ##
=======================================
  Coverage   93.29%   93.30%           
=======================================
  Files          91       91           
  Lines       11068    11083   +15     
=======================================
+ Hits        10326    10341   +15     
  Misses        742      742           

Flag	Coverage Δ
linux	93.16% <100.00%> (+<0.01%)	⬆️
pypy	93.30% <100.00%> (+<0.01%)	⬆️
windows	93.28% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
astroid/nodes/as_string.py	97.01% <100.00%> (+0.06%)	⬆️
astroid/nodes/node_classes.py	94.97% <100.00%> (+0.01%)	⬆️
astroid/rebuilder.py	98.21% <100.00%> (ø)

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[Pierre-Sassoulas]

Look great, let's wait for another reviewer's opinion before merging.

[DanielNoord]

Thanks!