Update PlotApi to use StorageApi for fetching data

[eqbech]

Issue
Resolves #14244

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')

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[codspeed-hq]

Merging this PR will not alter performance

✅ 36 untouched benchmarks

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_{Comparing replace-plot-api-with-storage-api (8da2d38) with main (67dc075)}

[ertomatic]

Screenshots differ from baselines. A baseline update PR has been prepared: equinor/ert-testdata#96

[ertomatic]

Screenshot tests now pass. The baseline update PR equinor/ert-testdata#96 has been closed.

[ertomatic]

Screenshots differ from baselines. A baseline update PR has been prepared: equinor/ert-testdata#97

[codecov-commenter]

Codecov Report

❌ Patch coverage is 72.97297% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.84%. Comparing base (be86c49) to head (3bf2e5e).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/ert/gui/plotting/plot_api.py	70.76%	38 Missing ⚠️
src/ert/gui/plotting/plot_window.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14270      +/-   ##
==========================================
+ Coverage   90.81%   90.84%   +0.03%     
==========================================
  Files         497      497              
  Lines       36062    36014      -48     
==========================================
- Hits        32750    32718      -32     
+ Misses       3312     3296      -16     

Flag	Coverage Δ
cli-tests	35.71% <5.40%> (+0.04%)	⬆️
fuzz	43.85% <10.13%> (+<0.01%)	⬆️
gui-tests	58.25% <64.86%> (+0.11%)	⬆️
performance-and-unit-tests	81.01% <68.91%> (-0.04%)	⬇️
test	45.27% <10.13%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
src/ert/services/ert_client.py	78.83% <100.00%> (+3.64%)	⬆️
src/ert/services/shared_client.py	68.68% <100.00%> (+13.84%)	⬆️
src/ert/gui/plotting/plot_window.py	78.65% <33.33%> (-0.05%)	⬇️
src/ert/gui/plotting/plot_api.py	80.40% <70.76%> (+0.20%)	⬆️

... and 2 files with indirect coverage changes

[ertomatic]

Screenshot tests now pass. The baseline update PR equinor/ert-testdata#97 has been closed.

[ertomatic]

Screenshot tests now pass. The baseline update PR equinor/ert-testdata#103 has been closed.

[ertomatic]

Screenshots differ from baselines. A baseline update PR has been prepared: equinor/ert-testdata#108

[ertomatic]

Screenshot tests now pass. The baseline update PR equinor/ert-testdata#108 has been closed.

[Copilot]

🟡 Changes recommended

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR refactors the GUI plotting layer (PlotApi/PlotWindow) to fetch data via the shared storage-server client (ErtClient/SharedClient) instead of using ad-hoc HTTP client creation, aligning with issue #14244’s goal of a single reusable client for the shared server.

Changes:

• Update PlotApi to use ErtClient for experiments/ensembles/parameters/responses/gradients/observations, and move caching to per-PlotApi instance caches.
• Update PlotWindow and related tests to call instance methods (api.data_for_parameter(...), etc.) instead of static cached functions requiring ens_path.
• Add SharedClient.close_client() and ensure GUI UI tests reset the process-wide shared client between tests.

File summaries

File	Description
tests/ert/unit_tests/gui/tools/plot/test_plot_window.py	Adjust PlotWindow tests to mock PlotApi instance methods and updated data_for_parameter signature.
tests/ert/unit_tests/gui/tools/plot/test_plot_api.py	Adapt PlotApi tests to new client plumbing by monkeypatching ErtClient.get_client and escaping behavior.
tests/ert/unit_tests/gui/tools/plot/conftest.py	Provide PlotApi fixture using an injected ErtClient wrapper over a mock request client.
tests/ert/ui_tests/gui/conftest.py	Add an autouse teardown fixture to close/reset the process-wide SharedClient between GUI UI tests.
tests/ert/performance_tests/test_dark_storage_performance.py	Update performance test client wiring to match ErtClient-based PlotApi behavior.
src/ert/services/shared_client.py	Add SharedClient.close_client() for explicit lifecycle reset of the singleton client.
src/ert/services/ert_client.py	Switch parquet decoding/caching to pandas DataFrames and expose DataFrame-returning endpoints.
src/ert/gui/plotting/plot_window.py	Use PlotApi instance methods for data fetching (no longer passes ens_path into static functions).
src/ert/gui/plotting/plot_api.py	Replace direct HTTP calls with ErtClient calls and implement per-instance caching wrappers.

Review details

• Files reviewed: 9/9 changed files
• Comments generated: 2
• Review effort level: Lite

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[berland]

git commit body says "format". That is probably not intentional and can be improved.