Update field_statistics to use individual ertbox per zone

[oddvarlia]

Closes: #842

[codecov-commenter]

Codecov Report

❌ Patch coverage is 67.21311% with 80 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.28%. Comparing base (3317bd1) to head (42744f6).
⚠️ Report is 16 commits behind head on main.

Files with missing lines	Patch %	Lines
src/subscript/field_statistics/field_statistics.py	67.21%	80 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #858      +/-   ##
==========================================
- Coverage   84.51%   84.28%   -0.23%     
==========================================
  Files          49       49              
  Lines        7349     7528     +179     
==========================================
+ Hits         6211     6345     +134     
- Misses       1138     1183      +45     

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[alifbe]

Not quite sure if the files in ensemble/share/grid_statistics/ are all needed.

In general, we should avoid code repetitions.

[Copilot]

Pull request overview

Extends field statistics to support zone-specific ERTBOX grids and temporary fields.

Changes:

• Adds per-zone/default ERTBOX configuration and processing.
• Updates RMS loading and statistics generation.
• Expands test data and reference outputs.

Reviewed changes

Copilot reviewed 5 out of 61 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/subscript/field_statistics/field_statistics.py	Implements per-zone ERTBOX support.
tests/test_field_statistics.py	Expands statistics tests and fixtures.
tests/testdata_field_statistics/config_example.yml	Demonstrates the new configuration.
tests/testdata_field_statistics/ensemble/share/grid_statistics/referencedata2/result_field_files.txt	Lists expected geogrid outputs.
tests/testdata_field_statistics/ensemble/share/grid_statistics/referencedata2/temporary_field_files.txt	Lists expected temporary-field outputs.

Suppressed comments (2)

src/subscript/field_statistics/field_statistics.py:1353

• The default grid is read earlier using the configured name verbatim, but this copy step uppercases it. A valid custom default such as ertbox_global.EGRID therefore passes sizing and then fails here looking for ERTBOX_GLOBAL.EGRID. Use the configured filename consistently.

        ertbox_file = Path(ertbox_config_path) / Path(ertbox_default.upper() + ".EGRID")

src/subscript/field_statistics/field_statistics.py:1924

• initial_relative_path comes from YAML as a string, so using / on it raises TypeError before any iteration-0 field can be read (the test config also supplies a string). Convert it to Path before joining.

            full_param_filename = init_path / Path(param_filename)

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[alifbe]

The code is rather huge so it's a bit hard to do prop review. But looks good from what I can see. 👍

Suggest to replace assertion with exception.