Add unit test for DilutePlanckianRadiationField (GSoC 2026 Eval)

[PritamHazra2708]

📝 Description

Type: 🚦 testing

This PR adds a unit test for the DilutePlanckianRadiationField class as part of the GSoC 2026 Evaluation Task.

Key Context & Implementation Details:

• Created test_dilute_planckian_radiation_field in tardis/plasma/tests/test_dilute_planckian.py.
• Adapted the test to align with the recent tardisbase refactoring.
• Integrated necessary Astropy units (u.K for temperature and u.Hz for frequency) to ensure strict unit compliance.
• Utilized the updated .calculate_mean_intensity(nu=nu) method, passing the required frequency array instead of the older parameter-less .calculate() method.

📌 Resources

• GSoC 2026 Applicant Evaluation Task.

🚦 Testing

How did you test these changes?

• Testing pipeline
• Other method (describe): Tested locally using pytest. Successfully generated local reference data using the --generate-reference flag along with --tardis-regression-data to ensure accurate regression matching without committing large data files to the repository.
• My changes can't be tested (explain why)

☑️ Checklist

• I requested two reviewers for this pull request
• I updated the documentation according to my changes
• I built the documentation by applying the build_docs label

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[tardis-bot]

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Hi human,
I ran ruff on the latest commit (e56e763).
Here are the outputs produced.
Results can also be downloaded as artifacts here.
Summarised output:

Details

1	F401	[*] unused-import
1	I001	[*] unsorted-imports
Found 2 errors.
[*] 2 fixable with the `--fix` option.

Complete output(might be large):

Details

tardis/plasma/tests/test_dilute_planckian.py:1:1: I001 [*] Import block is un-sorted or un-formatted
tardis/plasma/tests/test_dilute_planckian.py:1:8: F401 [*] `pytest` imported but unused
Found 2 errors.
[*] 2 fixable with the `--fix` option.

[atharva-2001]

This is not complete, you can move this to draft until then. Also can you mention the project and the idea. Also please follow the instructions, look carefully at the checklist