Enable interpolation of time-varying input data with temporal controller

[EdHone]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: @mo-lucy-gordon

Part of the work in #243.
The previous devlopments on the temporal controller object in #230 enable use to always have the correct data for the model time whilst maintaining the performance benefits and efficiency of the temporal controller. This PR implements basic linear interpolation of the input data at a user-specified time frequency. The changes include:

• developments to lfric_xios_temporal_mod to enable the interpolation
• a new mechanism for parsing user-specified time information using enums (and a unit test)
• two new integration tests which test the interpolation mechanism

Plot showing data validity of field read in using temporal controller and interpolated with a user-defined frequency

closes #242

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
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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)
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trac.log

Test Suite Results - lfric_core - lfric_core-242-temporal-interpolation/run4

Suite Information

Item	Value
Suite Name	lfric_core-242-temporal-interpolation/run4
Suite User	edward.hone
Workflow Start	2026-03-16T14:02:06
Groups Run	developer

Dependency	Reference	Main Like
lfric_core	EdHone/lfric_core@242-temporal-interpolation	False
SimSys_Scripts	MetOffice/SimSys_Scripts@2025.12.1	True

Task Information

✅ succeeded tasks - 389

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Performance Impact

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AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

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PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the TCD Team

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
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• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
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• Security considerations have been addressed
• Performance impact is acceptable