ULTRA l1b: Validation result updates

[lacoak21]

Change Summary

closes #3132

Overview

There were subtle differences in Bob's vs my code in how our masks were getting propagated and passed through. This PR aligns our code exactly.

File changes

Testing

Update stats test.

[Copilot]

Pull request overview

Aligns ULTRA L1B culling/validation behavior to eliminate subtle differences in how quality-flag masks are propagated through the extendedspin culling sequence (per #3132).

Changes:

• Adjusts how the cull “mask” is constructed/updated in calculate_extendedspin() before running upstream-ion/spectral/statistical-outlier culls.
• Updates the ULTRA45 Earth keepout angle threshold constant used in valid-event filtering.
• Updates the unit test expectations for flag_statistical_outliers().

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
imap_processing/ultra/l1b/ultra_l1b_culling.py	Minor whitespace-only change near valid-events helper logic.
imap_processing/ultra/l1b/extendedspin.py	Updates mask propagation/order for subsequent culls (upstream ion, spectral, stat outliers).
imap_processing/ultra/constants.py	Changes ULTRA45 Earth keepout angle threshold from 20° to 15°.
imap_processing/tests/ultra/unit/test_ultra_l1b_culling.py	Updates assertions around std_diff returned by flag_statistical_outliers().

Comments suppressed due to low confidence (1)

imap_processing/ultra/l1b/extendedspin.py:125

• upstream_ion_qf_2 is computed using the same mask as the first upstream-ion pass. Since flag_upstream_ion expects mask to represent bins flagged in previous steps, the second pass likely should also exclude bins flagged by the first pass (and/or high-energy). Otherwise the second channel set may be biased by bins already identified as upstream-ion contaminated.

    upstream_ion_qf_2 = flag_upstream_ion(
        de_dataset,
        spin_tbin_edges,
        energy_ranges,
        mask,
        UltraConstants.UPSTREAM_ION_ENERGY_CHANNELS_2,
        instrument_id,
    )

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