3165 bug hi l2 problems propegating error and uncertainty in maps

[tmplummer]

Change Summary

Overview

Fix NaN propagation issues in Hi L2 ena_intensity_stat_uncert and ena_intensity_sys_err variables.

Changes

imap_processing/ena_maps/utils/corrections.py

• Fixed negative flux clamping to use xr.where() instead of .where() method to ensure proper NaN preservation during the clamping operation

imap_processing/hi/hi_l2.py

• calculate_ena_intensity(): Added np.errstate(divide="ignore") context manager around systematic error calculation to suppress divide-by-zero warnings when exposure is zero (result correctly becomes NaN)
• combine_calibration_products(): Added skipna=False to the quadrature sum of systematic errors to ensure NaN values propagate correctly rather than being silently ignored

imap_processing/tests/ena_maps/test_corrections.py

• Added test_nan_input_propagation() to verify that NaN inputs in flux, statistical uncertainty, and systematic error properly propagate to NaN outputs during heliocentric frame interpolation

imap_processing/tests/hi/test_hi_l2.py

• Added test_combine_maps_handles_nan_uncertainties() to verify that when one map has NaN in ena_intensity_stat_uncert, the combined result correctly uses only the valid map's values

Closes: #3165

[Copilot]

Pull request overview

This PR addresses NaN propagation bugs in Hi L2 ENA map uncertainty/error variables, ensuring that NaNs are preserved through interpolation, clamping, and calibration-product/map combination logic.

Changes:

• Preserve NaNs when clamping negative interpolated flux values by switching to xr.where.
• Adjust Hi L2 systematic error computation and calibration-product systematic error aggregation to avoid incorrect non-NaN outputs.
• Add regression tests covering NaN propagation in heliocentric interpolation and NaN handling during map combination.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
imap_processing/ena_maps/utils/corrections.py	Updates negative-flux clamping to preserve NaNs during heliocentric-frame interpolation.
imap_processing/hi/hi_l2.py	Tweaks systematic error computation (warning suppression) and systematic error aggregation across calibration products.
imap_processing/tests/ena_maps/test_corrections.py	Adds a test verifying NaN inputs propagate to NaN outputs through interpolation.
imap_processing/tests/hi/test_hi_l2.py	Adds a test ensuring NaN statistical uncertainties don’t poison combined-map results.

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