Add extra=forbid to pydantic basemodels in ert run models and cleanup

[erlenlh]

Issue
Resolves #13518

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

• PR title captures the intent of the changes, and is fitting for release notes.
• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.
• Make sure unit tests pass locally after every commit (git rebase -i main --exec 'just rapid-tests')

When applicable

• When there are user facing changes: Updated documentation
• New behavior or changes to existing untested code: Ensured that unit tests are added (See Ground Rules).
• Large PR: Prepare changes in small commits for more convenient review
• Bug fix: Add regression test for the bug
• Bug fix: Add backport label to latest release (format: 'backport release-branch-name')

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.58%. Comparing base (cc26b7e) to head (b21db92).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13519      +/-   ##
==========================================
+ Coverage   89.57%   89.58%   +0.01%     
==========================================
  Files         466      468       +2     
  Lines       32962    32977      +15     
==========================================
+ Hits        29526    29544      +18     
+ Misses       3436     3433       -3     

Flag	Coverage Δ
cli-tests	35.67% <100.00%> (-0.03%)	⬇️
fuzz	43.94% <100.00%> (+0.02%)	⬆️
gui-tests	59.77% <100.00%> (+0.01%)	⬆️
performance-and-unit-tests	78.11% <100.00%> (+0.01%)	⬆️
test	45.41% <100.00%> (+0.02%)	⬆️

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

Files with missing lines	Coverage Δ
src/ert/run_models/event.py	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing ert-runmodels-update-basemodel (ff0bb85) with main (0175a5d)}

[jonathan-eq]

This should be safe. Very good 👍