Enable lfric_xios_file_type to take configuration from an associated XIOS field group

[Ed Hone (EdHone)]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: mo-marqh

This brings together the use of XIOS field groups within the lfric_xios_file_type. This will enable applications to configure the behaviour of fields within a file, without needing large-scale code changes within the model code itself.

By default an XIOS field group with the ID {FILE_ID}_fields will be created for each file defined with a lfric_xios_file_type object. This default ID can be overwritten by passing the field_group_id argument to the lfric_xios_file_type constructor. If this field group is already defined within an XML configuration it wont be overwritten so any fields contained with that field group can be configured by the model at run time.

I also fixed the iodef files in the lfric-xios integration tests to make them runnable with XIOS 3

closes #351

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• I have tested this change locally, using the LFRic Core rose-stem suite
• If required (e.g. API changes) I have also run the LFRic Apps test suite using this branch
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
• I have added tests to cover new functionality as appropriate (e.g. system tests, unit tests, etc.)
• Any new tests have been assigned an appropriate amount of compute resource and have been allocated to an appropriate testing group (i.e. the developer tests are for jobs which use a small amount of compute resource and complete in a matter of minutes)

trac.log

Test Suite Results - lfric_core - lfric_core-351-file-field_group/run2

Suite Information

Item	Value
Suite Name	lfric_core-351-file-field_group/run2
Suite User	edward.hone
Workflow Start	2026-04-29T08:50:48
Groups Run	developer

Dependency	Reference	Main Like
lfric_core	EdHone/lfric_core@351-file-field_group	False
SimSys_Scripts	MetOffice/SimSys_Scripts@cab3315	True

Task Information

✅ succeeded tasks - 390

I've also run these changes against lfric_apps

Test Suite Results - lfric_apps - lfric_apps-test_field_groups/run3

Suite Information

Item	Value
Suite Name	lfric_apps-test_field_groups/run3
Suite User	edward.hone
Workflow Start	2026-04-29T09:31:38
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.03.2	True
jules	MetOffice/jules@2026.03.2	True
lfric_apps	EdHone/lfric_apps@test_field_groups	False
lfric_core	EdHone/lfric_core@351-file-field_group	True
moci	MetOffice/moci@2026.03.2	True
SimSys_Scripts	MetOffice/SimSys_Scripts@cab3315	True
socrates	MetOffice/socrates@2026.03.2	True
socrates-spectral	MetOffice/socrates-spectral@2026.03.2	True
ukca	MetOffice/ukca@1cdb9c2	True

Task Information

✅ succeeded tasks - 1185

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Performance Impact

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Sci/Tech Review

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Code Review

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