ULTRA l1b upstream ion culling algorithm

[lacoak21]

Change Summary

closes #2914

Overview

Add the upstream ion cull algorithm and remove events at l1c that are flagged with these.

File changes

Testing

Validation test. Check the expected flags against Bobs code.

[Copilot]

Pull request overview

Adds an ULTRA L1B “upstream ion” spin-bin culling algorithm and propagates its flags into the existing quality-flag filtering pipeline so L1C can drop affected events.

Changes:

• Implement flag_upstream_ion() and wire it into calculate_extendedspin() (two-pass channel selection).
• Expose new upstream-ion quality flags as energy-dependent spin filters for downstream rejection.
• Add/adjust unit + validation tests, plus test data plumbing updates.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
imap_processing/ultra/l1b/ultra_l1b_culling.py	Adds upstream-ion flagging algorithm using summed counts across selected energy channels.
imap_processing/ultra/l1b/quality_flag_filters.py	Registers new upstream-ion quality arrays for energy/spin-dependent filtering.
imap_processing/ultra/l1b/extendedspin.py	Runs upstream-ion culling in extendedspin generation and outputs quality_upstream_ion_1/2.
imap_processing/ultra/constants.py	Adds constants for upstream-ion channel sets and sigma threshold.
imap_processing/tests/ultra/unit/test_ultra_l1b_culling.py	Adds upstream-ion validation test + refactors repoint-47 setup.
imap_processing/tests/ultra/unit/test_spacecraft_pset.py	Updates test input datasets to include theta/phi fields.

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[subagonsouth]

Clean, well organized code! LGTM.