Add extra=forbid to pydantic basemodels in ert config and cleanup

[erlenlh]

Issue
Resolves #13498

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 90.09%. Comparing base (a139c58) to head (eaaa544).
⚠️ Report is 22 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13501      +/-   ##
==========================================
+ Coverage   89.37%   90.09%   +0.72%     
==========================================
  Files         469      468       -1     
  Lines       33391    33408      +17     
==========================================
+ Hits        29843    30100     +257     
+ Misses       3548     3308     -240     

Flag	Coverage Δ
cli-tests	35.79% <100.00%> (+0.03%)	⬆️
fuzz	43.38% <100.00%> (-0.06%)	⬇️
gui-tests	59.27% <100.00%> (-0.07%)	⬇️
performance-and-unit-tests	77.82% <100.00%> (-0.01%)	⬇️
test	46.07% <100.00%> (+1.09%)	⬆️

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

Files with missing lines	Coverage Δ
src/ert/config/distribution.py	99.11% <100.00%> (-0.01%)	⬇️
src/ert/config/ensemble_config.py	97.08% <100.00%> (ø)
src/ert/config/ert_config.py	95.80% <100.00%> (ø)
src/ert/config/everest_control.py	87.50% <100.00%> (-0.16%)	⬇️
src/ert/config/forward_model_step.py	98.66% <100.00%> (ø)
src/ert/config/gen_data_config.py	95.57% <ø> (ø)
src/ert/config/model_config.py	100.00% <100.00%> (ø)
src/ert/config/parameter_config.py	98.41% <100.00%> (ø)
src/ert/config/response_config.py	97.87% <100.00%> (ø)
src/ert/config/summary_config.py	96.42% <ø> (ø)
... and 1 more

... and 18 files with indirect coverage changes

[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

---

_{Comparing ert-config-pydantic-base-model-update (94eca0f) with main (fab64f3)}

[Copilot]

Pull request overview

This PR tightens ERT configuration validation by setting several Pydantic BaseModel-based config classes to extra="forbid", preventing silent acceptance of unknown fields and cleaning up affected call sites/tests.

Changes:

• Enforce extra="forbid" on multiple ERT config models (e.g., ErtConfig, ModelConfig, EnsembleConfig, ParameterConfig, etc.).
• Remove now-invalid “extra” constructor fields from unit tests and strategies (e.g., random_seed, eclbase_format_string, nx/ny/nz, mask_file).
• Simplify some config model definitions by replacing model_config = ConfigDict(extra="forbid") with class-level extra="forbid".

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/ert/unit_tests/run_models/test_model_factory.py	Removes now-forbidden extra ctor arg (random_seed) when building ErtConfig in tests.
tests/ert/unit_tests/run_models/test_experiment_serialization.py	Updates Hypothesis strategies to stop passing forbidden extra fields into config models.
tests/ert/unit_tests/config/test_field.py	Removes mask_file from Field(...) construction in test helper.
src/ert/run_models/everest_run_model.py	Updates Everest → ERT runpath config creation to align with config model field changes.
src/ert/config/parameter_config.py	Sets ParameterConfig to forbid extra fields.
src/ert/config/model_config.py	Sets ModelConfig to forbid extra fields.
src/ert/config/forward_model_step.py	Sets ForwardModelStepDocumentation to forbid extra fields.
src/ert/config/everest_control.py	Sets SamplerConfig to forbid extra fields; removes redundant ConfigDict usage/import.
src/ert/config/ert_config.py	Sets ErtConfig to forbid extra fields.
src/ert/config/ensemble_config.py	Sets EnsembleConfig to forbid extra fields.
src/ert/config/distribution.py	Converts model_config = {"extra": "forbid"} to class-level extra="forbid".
src/ert/config/derived_response_config.py	Sets DerivedResponseConfig to forbid extra fields.

Comments suppressed due to low confidence (1)

src/ert/run_models/everest_run_model.py:340

• summary_fm.results.file_name is captured as eclbase above, but it is no longer propagated into runpath_config (now via summary_file_base_name). This means .res_runpath_list and the <ECLBASE>/<ECL_BASE> substitutions fall back to defaults even when the Everest config specifies a summary base name, which can break workflows expecting the runpath list to contain the simulator case base and can desynchronize simulator output naming vs response reading. Consider setting summary_file_base_name on ErtModelConfig when summary_fm is present (and/or ensuring it matches the SummaryConfig input base).

        runpath_config = ErtModelConfig(
            num_realizations=len(everest_config.model.realizations)
            if everest_config.model.realizations is not None
            else 1,
            runpath_format_string=str(