Type check ert.gui.ertwidgets

[eivindjahren]

Adds more type checking to ert.gui.ertwidgets

• [x] PR title captures the intent of the changes, and is fitting for release notes.
• [x] Added appropriate release note label
• [x] Commit history is consistent and clean, in line with the contribution guidelines.
• [x] Make sure tests pass locally (after every commit!)

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: Create Backport PR to latest release

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.30159% with 16 lines in your changes missing coverage. Please review.

Project coverage is 86.96%. Comparing base (f29176b) to head (b9594d0). Report is 5 commits behind head on main.

Files	Patch %	Lines
src/ert/gui/ertwidgets/checklist.py	66.66%	6 Missing :warning:
src/ert/gui/ertwidgets/searchbox.py	55.55%	4 Missing :warning:
src/ert/gui/ertwidgets/closabledialog.py	66.66%	2 Missing :warning:
src/ert/gui/ertwidgets/statusdialog.py	75.00%	2 Missing :warning:
src/ert/gui/ertwidgets/ensemblelist.py	0.00%	1 Missing :warning:
src/ert/gui/tools/file/file_dialog.py	80.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8166 +/- ## ========================================== + Coverage 86.62% 86.96% +0.33% ========================================== Files 384 384 Lines 23831 23905 +74 Branches 618 618 ========================================== + Hits 20644 20788 +144 + Misses 3107 3036 -71 - Partials 80 81 +1 ```

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